add a static flag to force writing LV2 state

add a static flag to force writing LV2 state

This is needed for save-as and archiving, LV2 state may not be saved
otherwise if lilv_state_equals() returns true.

Also if thestate is saved as part of save-as or archiving or
template, the state-version did increase.
Upcoming normal save will reference a plugin state that does not exist
in the current session bundle.