Option to exit after printing

Summary:
When running okular with the parameter --print to directly open the print mode, it doesn't exit after acknowledging the print dialog. Hence adding --print_and_exit option exits Okular after acknowledging the print dialog and thus is useful for the command line batch processing or a Dolphin service as the issue suggests.

FEATURE: 318998

Test Plan:
1. open a file in Okular using the parameter --print. It will open Okular in print mode with the print dialog
2. Either print the file or cancel the print dialog
3. You will find that Okular stays open
4. Now using this patch, see for available options with the --help parameter. You will find --print_and_exit option
5. Now open a file in Okular using the parameter --print_and_exit. It will open Okular in print mode with the print dialog
6. Either print the file or cancel the print dialog
7. You will find that Okular closes after acknowledging the dialog

Reviewers: aacid, #okular, ngraham

Subscribers: ltoscano, ngraham, a...