Dotcase: Improve exception-handling

Don't catch generic Exception, and log exceptions as errors. Also,
remove try-catch blocks around things which seemingly do not throw any
exception.

Change-Id: I333be1f178fec12f38caded0c176c93f6ed710b1
Dotcase: Only check for new notifications before displaying them

Rather than check for new notifications on every redraw, only check at
the beginning of each animation cycle (i.e., right before they're
about to be shown). This reduces notification checks from about twice
per second to about every 3 seconds.

Change-Id: Ia53de5bc24f3e41d33bfe5bc7c0f56b284e4d3e8