[api] cache the result of project_or_package_link

To make this work, I added a new model CacheLine that remembers in the
database if something for a package or project was cached. If that
package is changed, the event creation will then delete the cache line
[api] try to fix coverage results
[webui] move the assets into the main app - they end up in /public anyway
[api] pimp the coverage by fixing a typo :)
Merge README.setup into README.md
Update README.md
[dist] memcache is not required to keep session data
[api] support source update hook via token

can be used for example for a github service integration
[api] ensure that users in state deleted are not visible
[api][webui] fix (dummy) webui login handling

small refactoring
Add production frontend setup to the README
[api] fix token trigger using payloads like github.com.

use standard base64 tokens
[api] define package container via URL for service trigger
[api] fix crash when operating on not existing token
[backend] adapt rebuildkiwiproduct code to partition case

It was forgotten when all the other places got adapted.
[webui] increase coverage by removing functions
[api] allow nobody to query everything he's not forbidden to do
[webui] test 'download logfile'
[api] fix some issues reported by brakeman

and use escape_utils, see benchmarks on https://github.com/brianmario/escape_utils
[api] update gem versions