Update show sidebar images

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Add info about developer tools to guide

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Guide: Add listing of actions

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Guide: How to trigger actions on command line

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Split out show_main_window() from init_gui()

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>