Added support for running scripts as queries

Added a new connection type called 'script'.

It allows running scripts that returns the same JSON format as other data sources. The data is received by printing it to the standard output.

To configure it CONNECTION_STRING must be a path under which the scripts exist. Each script must be flagged for execution.

To run a script create a new query and enter the filename of the script (the path will be automatically concatenated).

Safety Features:
* Runs without shell (shell=False)
* Will only run scripts in the configured directory (or something that resides in a subdirectory).
* If the scripts folder is sufficiently protected and only authorized personnel can add scripts to it - it should be relatively safe.




Added support for a connection type called 'url'.

It allows settings URL to retrieve JSON results with the same format as other query runners.
To run a query, the query itself needs to be the URL.
If CONNECTION_STRING is set it will be used as the base URL to which the query is appended. In that case it will enforce that the query is a relative path to the base URL set in CONNECTION_STRING.