Remove built assets from repo, updates to docs + GH templates (#1955)

* Revamp issue and pull request templates, other docs tweaks

`yarn test` now runs all of our tests.

* Remove generated files from the repository

* Update to new Signal support URL

* Prevent the 'Test failed 2 == 1' from test-release in CI

* Another attempt to fix grunt test-release on Appveyor

* grunt test-release: Fail build if test fails

* Lint fix, and move jshint earlier in CI process

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,27 +1,37 @@
+<!--
+Thanks for contributing to the project!
+Please help us keep this project in good shape by going through this checklist.
+Replace the empty checkboxes [ ] below with checked ones [X] as they are completed
+Remember, you can preview this before saving it.
+-->
+
 <!-- You can remove this first section if you have contributed before -->
-### First time contributor checklist
-<!-- replace the empty checkboxes [ ] below with checked ones [x] accordingly -->
+
+### First time contributor checklist:
 - [ ] I have read the [README](https://github.com/WhisperSystems/Signal-Desktop/blob/master/README.md) and [Contributor Guidelines](https://github.com/WhisperSystems/Signal-Desktop/blob/master/CONTRIBUTING.md)
 - [ ] I have signed the [Contributor Licence Agreement](https://whispersystems.org/cla/)
 
-### Contributor checklist
-<!-- replace the empty checkboxes [ ] below with checked ones [x] accordingly -->
-- [ ] My contribution is fully baked and ready to be merged as is
-- [ ] My changes are rebased on the latest master branch
-- [ ] My commits are in nice logical chunks
-- [ ] I have followed the [best practices](http://chris.beams.io/posts/git-commit/) in my commit messages
-- [ ] I have tested my contribution on these platforms:
- * GNU Hurd 1.0, Chrom{e,ium} X.Y.Z
- * Amiga OS 3.1, Chrom{e,ium} Z.Y
-- [ ] My changes pass all the [local tests](https://github.com/WhisperSystems/Signal-Desktop/blob/master/CONTRIBUTING.md#tests) 100%
-- [ ] I have considered whether my changes need additional [tests](https://github.com/WhisperSystems/Signal-Desktop/blob/master/CONTRIBUTING.md#tests), and in the case they do, I have written them
 
-----------------------------------------
+### Contributor checklist:
+- [ ] My commits are in nice logical chunks with [good commit messages](http://chris.beams.io/posts/git-commit/)
+- [ ] My changes are [rebased](https://medium.freecodecamp.org/git-rebase-and-the-golden-rule-explained-70715eccc372) on the latest [`development`](https://github.com/WhisperSystems/Signal-Desktop/tree/development) branch
+- [ ] My changes pass 100% of [local tests](https://github.com/WhisperSystems/Signal-Desktop/blob/master/CONTRIBUTING.md#tests)
+- [ ] My changes are ready to be shipped to users
+
 
 ### Description
-<!--
-Describe briefly what your pull request proposes to fix. Especially if you have more than one commit, it is helpful to give a summary of what your contribution as a whole is trying to solve.
-Also, please describe shortly how you tested that your fix actually works.
 
-Please note, that after you have submitted your PR, the Travis CI build check will fail. This is a known issue (#708) and you don't have to worry about it. (■_■¬)
+<!--
+Describe briefly what your pull request changes. Focus on the value provided to users.
+
+Does it address any outstanding issues in this project?
+  https://github.com/WhisperSystems/Signal-Desktop/issues?utf8=%E2%9C%93&q=is%3Aissue
+  Reference an issue with the hash symbol: "#222"
+  If you're fixing it, use something like "Fixes #222"
+
+Please write a summary of your test approach:
+  - What kind of manual testing did you do?
+  - Did you write any new tests?
+  - What operating systems did you test with? (please use specific versions: http://whatsmyos.com/)
+  - What other devices did you test with? (other Desktop devices, Android, Android Simulator, iOS, iOS Simulator)
 -->