"Clear all" button on recent apps

    Ported from ParanoidAndroid by zigackly:
    https://github.com/ParanoidAndroid/android_frameworks_base/commit/f8c44e6ef667a3ebe9b658f148fa78a8d4f9a8dd

    Add button to tablet layout ported from Codename Android by zigackly:
    https://github.com/CNA/android_frameworks_base/commit/8d259fe3588c261baa5a17c361255cf28cc82bfe

    Patch set 2: Make the layout consistent, with the button at the top right.

    Patch set 3: Remove the redundant use of removeTask()

    Patch set 4: Top right layout does not work in tablet mode: make it top left for tablets only.

    Patch set 5: Different implementation (No need to keep track of views) - Danesh M

    Patch set 6: Top left layout no longer works for tablet mode with new implementation.
                 Make it bottom left for tablets only.

Change-Id: Iceb86eef41160f1c17e51463b37fd97e27acfb2e