Rewrite installation process with interactive su shell

The main benefit is better error handling, especially detection of failure
to get root access.
Don't reinvent the wheel when concatinating text
Move version displaying to separate function
Handle install buttons asynchronously
Don't show module list update toast after install
Refresh versions even if (un)install failed

It might have worked partially, so the information can be incorrect. The
correct information would be displayed when re-entering the fragment,
which would be confusing.
Smaller font in install result dialog
remove shell scripts
Busybox: mkdir, reboot and sync applets
Signed disabler.zip with testkeys
Installation via recovery

With this, the Xposed app_process binary can be installed via a custom
recovery (CWM or TWRP). This is especially use full for HTC phones with
S-On, which reverts any changes to the /system partition on reboot.

The flashable zip contains shell script which creates the backup and then
copies the new app_process file from this location:
/data/data/de.robv.android.xposed.installer/bin/app_process.
Therefore, it is independent from the Xposed version and platform, doesn't
need to be generated dynamically and could also be used to restore Xposed
after ROM upgrades.

Still missing:
- GUI/settings to use the classical installation method as default and
  give the user a hint that he can switch to a different one in case of
  problems.
- Better summary when the installation via recovery has been prepared.
- Confirmation dialog before rebooting to recovery.
- More testing with different recoveries and devices.
Let's SimpleAdapter's context be Activity, not Application.

`DownloadsAdapter` will inflate layout, and layout should be under
`Activity`. Actually, current `XposedApp.getInstance()` is an
`Application` context, which doesn't apply custom theme. (Back-ported
version need custom theme).

For more question of context, I think this article describes clearly:
http://www.doubleencore.com/2013/06/context/
Add preferences for installation mode
Ignore PACKAGE_CHANGED for single components

The event is needed to detect e.g. if a package has been frozen, but it
can also occur if components (e.g. receivers) are disabled/enabled. Ignore
the event in these cases.
Display selected install mode in the framework section
Increased/unified fragment padding
Credits for libsuperuser
Keep su session open until navigating away
Offer reboot to recovery after installation
Store Xposed-Installer-Recovery.zip in /cache/recovery

This directory is cleaned up automatically on each boot by
RecoverySystem.handleAftermath(), so we don't need to take care of it.