front: Add logcat, date, shell utility functions.
front: Implement crash handler to save crash reports to disk.
libs: Update to ACRA dev build 4d15be3253c4e900abe320737790d78981e21ecf.

https://github.com/ACRA/acra/commit/4d15be3253c4e900abe320737790d78981e21ecf

This fixes an issue that became apparent after adding our extra crash
handler.  Two crash logs were being created, where the second was caused
by a bug in ACRA.

The bug is described here:
https://github.com/ACRA/acra/issues/136

and resolved here:
https://github.com/ACRA/acra/pull/165