Repo cleanup to comply with new catapult deploy process

- Added /dist/ folder to `.gitignore`
- Replaced references to version number with `XXX_VERSION_XXX`
- Replaced all-release `CHANGELOG.md` with per-release `changelog.txt`
- Removed `release.sh` script
- Added build task to `gulpfile.js`
- Updated `npm test` to build the distribution files before testing
- Updated the dist file header and made it preserved across both
minified and unmagnified files
Updated README badge to only show status of master branch
Replaced XXX_VERSION_XXX with 0.0.0

Using `XXX_VERSION_XXX` in the package.json caused `npm install` to
fail. So I’m replacing it with 0.0.0 which will allow `npm install` to
work and still be easy to replace during the deploy process.
Added `npm run travis` command to package.json
Cleaned up and fixed issues in README
Updated spacing in build header
Merge pull request #13 from firebase/jw-catapult

Repo cleanup to comply with new catapult deploy process