[api] fix configuration registration enums

"deny" for registration was not possible due to wrong DB setup (issue#669)
[backend] do not loop if a prp has a dep onto itself
[api] yet another place of wrong registration mode "deny"

adding also some test cases.

Thanks to Rick Liu for reporting this.
[api] follow with code quality check :/
[backend] add --volatile option for --clone-repository

copies the :full trees into a _volatile package so that the
entries are backed with the new full tree handling.
[webui] Hotfix logfile links on project#monitor. Nasty stuff..
[webui] do not show build log of source protected packages (as api does)

Conflicts:
	src/api/test/functional/webui/package_controller_test.rb
[webui] revert to codemirror 3 (for now)
[dist] README.SETUP: memcached is mandatory now

memcached is not optional anymore it is mandatory for the webUI to work.
[api][backend] log buildhistory of patchinfos and check last version got build before release

fixes bnc#879793
[dist] update gem versions
[backend] Optimize sourcedeletion function

Optimization done in runtime at revfile rewrite process and do
not fail if a project was deleted during (long) run
[backend] fix typo in update_dst_full refresh operation
[api] cleanup channel recreation code a bit
[backend] do not put imported binaries into patchinfos
[backend] be more careful with channels and patchinfos, they must not get put into useforbuild

Fixes the event_useforbuild handling as side effect...
[backend] fix nouseforbuild marker regeneragtion
[api] store channel set in package object
[dist] Update README for latest release

+ Clean up a couple of typos and trailing spaces.
[webui] Improvements in comment display

 * @user in the body is now a link
 * Use user_with_realname_and_icon to display the author
 * Mails are sent with multipart in plain text and html
 * Layout for the html version of the mails