Test against multiple AS and Sinatra versions

This enables testing against Sinatra Edge and multiple activesupport versions. The change also
lowers the activesupport dependency to 3.1.

Failures in Sinatra Edge tests are ignored
Less matrix entries for sinatra_edge and ActiveSupport

Travis is free, so don't tax it too much with matrix entries that don't give much gain.
Applied @DAddYE's suggestion on #783
Fixed admin generator to allow removing the admin (using it with -d).
Merge pull request #1013 from padrino/fix-admin-gen-delete

Fixed admin generator to allow removing the admin (using it with -d). It currently fails.
Remove deprecated dependency
Add Ruby 2.0 to .travis.yml
Merge pull request #1014 from tyabe/add_2-0-0_to_travis

Add Ruby 2.0 to .travis.yml
Merge remote-tracking branch 'origin/master' into multi-as-testing

Conflicts:
	.travis.yml
Merge pull request #1010 from padrino/let-rake-work-without-rspec

Let rake tasks work without rspec on production
Merge pull request #1003 from padrino/multi-as-testing

Test against multiple AS and Sinatra versions
Updated static assets
Added a missing dependency for padrino-helpers in padrino-cache. See #719.
Merge pull request #1021 from padrino/add-helpers-as-dependency-for-cache

Added a missing dependency for padrino-helpers in padrino-cache
Remove ree and 1.9.2 from testing, add rbx instead
Use ActiveSupport::JSON for dumping json in render

This relieves us of any extra work that comes with handling JSON engines, etc.
State rbx mode explicitely
Merge pull request #1022 from padrino/be-nicer-to-travis

Remove ree and 1.9.2 from testing, add rbx instead
Merge pull request #1025 from padrino/active-support-json

Use ActiveSupport::JSON for dumping json in render