Feature/use current location

Optionally show directions from current location.

Before transitioning to directions view, prompt user what origin to use (either entered address or current location), then show directions for selected origin.

In case current location selected but location services disabled, will prompt to enable location services, then re-query once location found.

Also changes redundant search button on home view to contact selector button.
Would be a bit more consistent with above and easier to parse if it was:
```
if (use_location) {
...
} else {
...
}