Make system read only show no matter what on first TWRP boot

Initial value for tw_mount_system_ro is now 2. If the value of
tw_mount_system_ro is 2 during boot, then we will show the system
read only prompt and ignore the value from the lifetime writes
check.

Note: Changed the value of FILE_VERSION which will trigger the
data manager to throw out previous settings and start with default
values so that existing TWRP users will get the prompt at least
once.

Change-Id: I447767b64617f855156a19a5dc15c4ece6dff7b8