propose to make uci commit more specific to minimize unwanted changes in other temporary written config files like wireless ssid (in some offline changers)

Use the common term; the "Expert Mode" never was a distinct mode of
operation anyways.

This new feature introduces the new uci section 'gluon-core.wireless' with a preserve_channels option:
 * preserve_channels (boolean)

By setting this option to 1 (true) wifi channels will be preserved during upgrades.

Fixes #574

fix typo and express sentence regarding update priority clearer

We'll soon have other output besides the images, having a single directory
for all output makes sense.

Fixes #376

the command autoupdate not work, so a fix smal fix necessary