This adds the differentiated left/right anchors for hdpi and further
tweaks the behavior of text anchors.
Highlights:
* New assets are translucent - increased visibility for whatever is
beneath.
* Start and end anchors may not cross one another.
* Minimum selection size is now 1.
* Touch targeting tweaked.
Change-Id: I601361323916ee19149562a23dc3242d908da45c
fbb3b4768e