Improvement: add command export and import function

[elkinaguas]

After migrating clir form using a json file to an sqlite DB to store commands #28 and #14. It seems like a good idea to add two new functions.

An export function that will save commands into a json format. I think @croketillo will like this one.

An import function that will allow to merge an exported json file into clir's database.

[elkinaguas]

Done #34