Add min letter count property
This is what we discussed in the last two minutes of our BoF.
By also adding it as a property to the desktop file we can make sure that dbus runners can also also use this feature with the current version of the interface. This way we can prevent useless thread spawning and also in the case of the dbus runners also useless dbus calls.
And this way the if statement for the minimum letter count of the query and the single runner mode does not need to be copy/pasted for every runner.