Add make reload task

`make reload` will perform a `quick_compile` and then rsync all files under `apps/ejabberd/ebin` into the highest-versioned `ejabberd-2*` directory in `./rel/mongooseim/lib/`. 

If the `reloader` app is running on the mongooseim node, then the relevant modules will get reloaded automagically. If not, then the shell command `l(ModuleName)` is your friend.

Currently, only `apps/ejabberd` is considered.