Allow passing search queries from the command line

Allow passing a search query to the running instance via the command line.

Using `zeal --query 'java|Hash'` will open a zeal window with a search for `java|Hash`. If an instance of zeal is already running it will be brought to front with the query and the first result highlighted. Otherwise a new instance will be started.


The purpose of this is to allow for easy integration of `zeal` into existing plugins for Dash.