[webui] Rename Home to Watchlist

Description of watchlist is also misleading

The thing shows only the watchlist nothing else, so there are no
involved projects, plus you can watch something even if you are not
involved.

Make the link empty for watchlist

Actually having no js is not working for obs at all so no need to
have working link here.
This actually solves the issue that javascript did watchlist, but
the nojs is pointing to the home page.
[api] check the verifymd5 instead of the srcmd5 against jobhistory

Also check the now fast lastfailures route for the md5sum first - saving considerable
time in repo checker
[webui] adapt the test suite to Benjamin's latest fixes

It actually verified the broken state before ;(
[api] fix the test suite for /status/bsrequest
[api] introduce clockwork to replace cron dependency

clockwork can run jobs more often than one minute, already runs
as same user and has the ruby stack already loaded, so it takes
way less resources all in all
[activexml] in case of error, return Xmlhash not hash
[api] store the last number from lastevents in the database

It is pretty much overkill to have a table for a single value,
but it might get useful in the future and the alternative is writing
a file and it feels so unrailsy