#19 the recently opened files paths get written to their own xml-file
#19 if the user chooses to open a file which does not exist, then do nothing
#19 RecentlyOpenedFilesList: cleaned up and comments
#19 WatergisOptionsPanel: removed code from Configurable methods + jalopy. Closes #19
Merge branch 'bug/19-recently-opened-files-list-behaviour' into dev