use constant for context flags
add verbose startup messages with correct prefix
simplify menu_info_submenu_type
fix indentation
exit successfully when run with --version
use of g_error is always fatal
add backtrace script
reorder functions according to header
stop using deprecated GtkStock
warn on unhandled updates
stop using deprecated GtkImageMenuItem

fixes #22
rename systray_add_menu_item to systray_add_item
split systray_add_menu_item function
split callback from menu_info_item_rename_dialog()
add support for managing pulseaudio modules

- list all modules
- unload module (from context menu)
split out placeholder handling
add/remove missing placeholders