Made possible to remove a tripplet from udev rule.

Also a minor refactoring is part of the commit. Started separating udev
functions into own file and so on.
Updated testsuite.
Changed default udev rule to one more suitable for device renaming.
Created helpers for setting one interface up / down.
Updated changelog and spec file.
Separated (and renamed) WriteUdevDriverRules

Separated into two functions. First writes per interface udev rules
(device renaming). Second writes per driver udev rules.
Added helper for getting iface's udev rule.
Fixed and refactored WriteUdevItemsRules.

Contains several improvements. Most important are
- when writing udev rule for particular interface, network service
needn't be stopped, setting iface down is enough
- udev rules are reloaded after writing them down, so the daemon
can reflect changes
- when trigger(ing) udev events, explicit action identification was
added (default has changed in the past from add -> change)
Added AddToUdevRule function.

It adds a tripplet into udev rule and does some basic check on it.
Extended testsuite for udev.
Refactoring WriteUdevDriverRules.

Driver's rule is created using AddToUdevRule function.
Merge pull request #102 from mchf/renaming_ifaces

Fix workflow (mainly handling udev changes) when renaming a device.