CRAFTERCMS-227: Delete should not be available when a content is locked

When a content is locked, the 'Delete' option is not available neither
in the contextual navigation nor in the "right-click" menu. Also, in
the case of bulk operations, if at least one content is locked within
all selected then the "Delete" option is not available either.
Merge remote-tracking branch 'david/master'
Merge remote-tracking branch 'david/master'
CRAFTERCMS-213
Removed not null constraint because Oracle treats empty string as null. Also added new Content Type constant for unknown type
Merge remote-tracking branch 'origin/CRAFTERCMS-213'
CRAFTERCMS-214
Added improved logging. Eliminate double locking on write content action.
Merge remote-tracking branch 'origin/CRAFTERCMS-214'
CRAFTERCMS-219
Sending notification from deployment engine were missing.
CRAFTERCMS-214
Added master repository lock (semaphore) to avoid deadlock.
Merge remote-tracking branch 'origin/CRAFTERCMS-214'
CRAFTERCMS-197
Unload event was trying to unlock content item regardless if it is new content or existing content
CRAFTERCMS-223: <br> and <hr> auto correction in RTE