settings: big cleanup

finally remove all dummy elements

move "themes" into the more section, together with "recent menu"
move contextional headers into notification drawer menu
fix System Update Settings action
remove all nameless gears references

cleanup settings

Change-Id: Ib2c18dfc58dc0103909dc4e1ec6e5e5862c86074
Signed-off-by: Alexander Martinz <eviscerationls@gmail.com>