add: basic layer save and load.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
update: make ArchiveFile global, since we need its dir name in Canvas;
add: option in configuration dialog to enable skip;
minor changes.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
fix: or more like a workaround, make messagebox in closeEvent of mainwindow show.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
fix: stacked layers when clear layers.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
change: static speed.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
update: translations.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
fix: update url.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
change: deferJob to delayJob;
change: async call using std::async;
change: more grace way to make recursive call, may help on stackover problem;
change: pause everything when user close mainwindow.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
Merge branch 'stacked_layers' into 0.4