fix(bpSref): remove bpSref, replace w/ uiSref

bpSref has always been an exact copy of uiSref, and its only purpose was to make it work w/ bpTap.
As we don't want to duplicate functionality any longer we'll be using and extending ui.router's original uiSref.

BREAKING CHANGE: bpSref is now named uiSref

before:
```html
<bp-action bp-sref="somestate"></bp-action>
```

after:
```html
<bp-action ui-sref="somestate"></bp-action>
```

This should be a search and replace migration.