feature request: more control via krop.conf file

[jeffkowalski]

The krop.conf file presently allows for configuration of several defaults.

I suggest adding more control, in two domains:

1. Reflect more UI settings. In particular, I suggest a setting in the conf file that reflects krop --selections individual. Consider adding a "SelectionsApplyTo" setting with the same "all,evenodd,individual" options as on the commandline. Similar too for the other UI options like "InitialPage"
2. Allow more flexible keyboard accelerators. For example, I would like to invoke "Quit" using "Escape", and "<Primary>w" (Ctrl-w).

See pdfarranger as an example of the suggested customizations.