Fixed photos grid displaying on new email creation/composing (bug introduced with "skip nophoto" option in version 0.8.

An option is added to addon settings to skip contacts without photo while generating photos grid

- fixed adding photos on options page;
- fixed working with AddressBook photos only (when local photos are not defined);
- code optimisation.
- added display photos in compose window.

Code improvements with access to photos on local filesystem.
On adding/removing photo files from directory - photos should be manually re-scanned on addon's options page.
Directory with photos should contain only one file per e-mail address (e.g. if both files with different extension like "[email protected]" and "[email protected]" present - error will appear on adding photos on addon's options page.