[IMP] server.py: --dev=reload with inotify

Add the alternative of inotify instead of watchdog to watch the addons
paths the server was started with.

Reason: watchdog spawns 2 threads per path to watch. When there are a
lot of addons paths, this can become too costly. With inotify we watch
all the repositories in a single thread.

https://github.com/dsoprea/PyInotify

installation:

    pip install inotify