[webui] Fix password/account changing
[backend] Add the feature to support multiple notify plugins

Signed-off-by: Hasan Wan <hasan.wan@intel.com>
[backend] Avoid endless rebuilds if qemu-linux-user is missing

A common error happening on the build.opensuse.org instance
is that buidl is enabled for armv7l, but no or not the right
qemu-linux-user is installed. In those cases the builds
are looping endlessly on the build cluster, wasting a lot of
CPU. Detect that case and end it.
[dist] Clean worker dirs on startup

Ensure that there is nothing left in there. Especially
when changing worker types there can be artefacts propagating
into the build (e.g. preinstallimages picking up previous
build root images)
[backend] always remove :dir directories when killing jobs
[backend] save memory by storing the meta as a single string instead of a string array

Makes things slightly slower, but the memory savings are much more
important than a few milliseconds.
[dist] Amazon EC2 tells the public hostname via an own command
[webui] ignore flash messages about binary protected statistics

_statistics are build results
[api] move code to find the default reviewers into the model
[api] move generation of patchinfo in the project model
[api] move the complete permission check in a function on its own

Using functions of the request and the action model
[api] have a subclass for each request type

This is just a rename of the column name, but this allows in the future
to have functions overload per type
[api] move action type specific code from the controller into the models
[backend] support qcow2 format publishing
[api] add the basics for a group request type
[api] create an official hook called during create of a request
[api] fixing and testing of group actions
[api] some more refactoring of requests and fixes for groups
[api,webui] fix ruby 2.0 reported problems and update gems
[api] support searching for grouped requests