Use libsmfm to resolve URLs.
Refactoring of pref.c. Removed lots of duplicated code.
Arrange options into 2 groups in configuration file: View and Edit.
Update copyright in pref.c
Import gtkcompat.h from lxpanelx
Drop support of gtk < 2.18, as libsmfm does not support it
Add "Show Toolbar" to Preferences dialog. Assign mnemonic keys to all items of the dialog.
Update toolbar visibility after closing Preferences dialog
Improve readability of create_nav_bar()
add option toolbar_on_top
Open context menu on Menu key press or F10.
Fix program termination.