Add new view for te Chek For Updates button

Ticket:	#6300
Fix typo in the name of the exception
Add dialog to the Apply Pending Updates button

Ticket:	#6300
Mount .system datasets under /var/db/system.

Change zfs mountpoint of .system datasets to 'legacy' and mount them
under /var/db/system instead of default location. From now on,
.system datasets are mounted manually by the system_dataset_create()
function.

Ticket:	#6284
A bit more logging information.
Do not depend on get_handler to show progress of file download
Testing revealed some typos, some thinkos, and some wtfs.
The system dataset is no longer a symlink.  Clean up the code at the same time.
Merge remote-tracking branch 'origin/master' into freebsd10