Automate gem updating

I've added a rake task to automatically check for newer versions, download them, and increment the gem version number. This should help reduce the tedium.

Also, the updater revealed two other issues which are fixed along with this PR.

1.  We no longer should include `angular-bootstrap`, since it is no longer part of the project
2.  We don't need (or want) the execute bit set on the asset files.