Use generic interval mechanism in most of the modules that use slow
updates.
Only exception: getcrypto, as the interval is specified in seconds there
and I want to retain backwards-compatibility.
fixes#220
If data cannot be retrieved for some reason (be pretty generous about
that by catching generic exceptions), instead of terminating the whole
status bar, simply report unknown data.
see #110
Since requests works the same for python2.7 and python3.x, use requests
instead of urllib (which returns a string in python2.7, but byte data in
python3.0, at least).
* Use app-specific API key for bumblebee-status
* Add some parameters (location, unit, update interval)
* Make interval calculation based on time, not number of calls