Create rundb host directory if necessary.

Closes #253. Validation of new suites (never been run yet) was failing
because the run-db host directory (default ~/cylc-run/SUITE/) did not
exist (The validation process instantiates tasks, which now results in
db creation).
Merge pull request #284 from hjoliver/253-create-rundb-dir

Create rundb host directory if necessary.
One user guide typo fixed.
Fix error on GUI color theme change for single view.

Theme change code did not know that one current view can be None.
Merge pull request #287 from hjoliver/bug-fix-theme-change

Fix error on GUI color theme change for single view.