schemas:dock:: rename legacy mode to classic mode
app:dock:: get tray icons back after restarting dde-dock.

call "RequireManageTrayIcons" method of com.deepin.dde.TrayManager.
res:dock:: fix tray icons is not shown problem.

reason:
the position is not right on startup.

solution:
delay to calculate the position on startup.
res:dock:: fix contextmenu problem.

the contextmenu is not shown.

reason:
backend is changed to use enum instead of string, however, frontend is not
changed.
res:dock:: fix typo