Settings: Implement ad blocker [3/3]

*Hosts File Manager
*Picked from Dirty Unicorns
*This uses two prebuilt hosts files and switches between them by symlinking

PS2: Commit msg
PS3: reverted to copying file instead of symlinking,
delete hosts file before copying to make sure to replace even an existing symlink,
set correct permissions after copying

AICP:
PS4: Rebase and add comments

Change-Id: Id3ff69373c871a2c4414180282386835a2d0f507