memory: add new dalvik fragment

Basically it works like the CPU governor panel; it adds dynamically
EditTextPreferences on a onClick-Event.
This will save a lot of space (and time) for the memory fragment.
The only missing thing are the correct set on boot settings, but this
should rather be easy.
aero: add better back navigation

When the user is located in soemthing like FragmenX -> FragmentY it is
not necessary to close the whole app when the back button is pressed.
Instead we are just jumping to the last fragment.
memory: cleanup unnecessary stuff

The swappiness and min_free preferences are now deprecated ad were
replaced by a previous commit.