Log Message:
mate-themes: update to 3.22.20

Change log:

### 3.22.20 (GTK 3.22)

  * Translations update
  * GreenLaguna: add selectable metacity theme with borders
  * BlackMATE: Restore 1px border metacity theme for the composited case
  * BlackMATE: add selectable metacity theme with borders
  * Submarine: add metacity themes with huge borders
  * Menta: add selectable metacity theme with borders
  * Change url project's website
  * GreenSubmarine: use menta icon theme
  * BlackMATE: provide enough border to resize windows with recent changes elsewhere
  * GreenLaguna: add metacity-theme-3.xml version back
  * include GtkStock icons directly in HCI
  * all themes: adjustments for headerbars
  * Update mate-desktop icon for ContrastHigh theme
  * Remove unused icons
  * Menta: metacity-3, rounded corners for modal-dialogs
  * Menta: improve GtkSwitch
  * Menta: improve metacity-theme-3
  * menta: GtkSwich, disable on/off characters
  * Rename gnome-power-manager.png to mate-power-manager.png