Revert "depend on activesuport"

This reverts commit a0f9bfdd3cfe34e65fb26f71913b983bc564694a.
weaken pdfkit dep
weaken hashie dep
weaken execjs dep
weaken kramdown dep
weaken diffy dep
weaken pdfkit dep
weaken execjs dep
add certs
revert deps as development for tests
depend on activesupport
fix duplicate dependency
typo in app generator
now really proper Gemfile for developers