Suite gcontrol button added to rose-edit.

- also fixed bug in rosie go if cylc gui icon path is None
Output viewer now added to rose edit toolbar.
Merge remote branch 'upstream/master' into 275
Basic functionality for metomi/rose#275 implemented.
Added in menu entries and moved handlers out to menu.
Fixed missing import.
Removed redundant code.
Import tidy.
Further import tidy.
Scheduler added to menus.
Merge remote branch 'upstream/master' into 275
Merge remote branch 'upstream/master' into 275
Review changes.
Whitespace tidy.
"_"'s added to init entries.
Merge remote branch 'upstream/master' into 275
Merge remote branch 'upstream/master' into 275
Merge pull request #390 from arjclark/275

275: add output viewer and launch gcontrol to rose edit