[api][backend][webui] fix route conflicts between /_status and /_jobstatus

document the _jobstatus api and add at least some very
basic tests for them.
[api] fix incorrect diffing on creation of submit requests with given target
[webui] Small fixes in the OBS specific markup

 * @user was not working at the very beginning of the comment.
 * Req# and SR# are now case insensitive (and Request# added)
[webui] catch some more exceptions to avoid 500 crashes in request handling
[api] handle diffing of new request to project linked targets correctly
[webui] avoid hanging live log page, when the worker allows TCP connect, but does not deliver data
[backend] enable caching of binaries when OBS instance is forwarding it for another instance.
[webui] do not crash when handling remote instance with invalid SSL CA

This happened when adding packman OBS instance and trying to add
a repository in the simple webui view.

Repository targets won't become visible anyway.
[webui] disagreement that this function is not readable anymore :(
[dist] Improve logging

Give more of a clue when unable to reach the rep server.
[webui] proper error handling for changing review state
[webui] proper error handling when superseding a request.
[backend] support definition of predecessor product name

bnc#883206
[backend] fix forwarding of full tree cpio requests

Only needed for "transitive interconnect" setups, which are currently
not really supported anyway. Still...
[backend] Obsoletes don't work on provides
[api] fix diffing on creating submit requests

The case when target package exists and source package is remote
[backend] enable vm watchdog in build script

Let's do it by default for all VM builds for now to avoid yet
another config option.
[api] don't crash when trying to submit to remote instance
[backend] allow to specify external pool repository URLs.

bnc#884270
[backend] ignore frozenlink if a specific srcmd5 is requested