Introduced empty-state handling for repos

Updated IDE view to show empty state

Introduced new `emptyRepo` getter to mark the empty projects

Added TOGGLE_EMPTY_STATE project's mutation type

Handle empty-repo state after the first commit

Moved getBranchData() out of Project actions. This action has to
be shared between both Project and Commit module, hence it needs
to be available from the top-level actions in IDE

Provide a dummy bootstrapping for a non-existent branch when setting
workingReference

When committing to an empty repo, fetch the branch information right
after the very first commit to set a proper reference on state

Switched flash to createFlash for error messge when getting
branch data

Re-factored openBranch action in Web IDE

- shortcut for rendering empty state right away
- do not attempt to fetch files alongside with
branchData as branch might not exist at all
- catch potential errors on both: fetching
branchData and getFiles