luci-themes: luci.main.mediaurlbase not set correctly

Currently by default theme Bootstrap is installed but
luci.main.mediaurlbase (it holds the current active theme) still has
openwrt.org set.
I did not find the mechanism how LuCI starts Bootstrap theme but the
installation should set luci.main.mediaurlbase correctly.

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>

themes/luci-theme-bootstrap/root/etc/uci-defaults/luci-theme-bootstrap

@@ -1,6 +1,7 @@
 #!/bin/sh
 uci batch <<-EOF
 	set luci.themes.Bootstrap=/luci-static/bootstrap
+	set luci.main.mediaurlbase=/luci-static/bootstrap
 	commit luci
 EOF
 exit 0

themes/luci-theme-freifunk-bno/root/etc/uci-defaults/luci-theme-freifunk-bno

@@ -1,6 +1,6 @@
 #!/bin/sh
 uci batch <<-EOF
 	set luci.themes.Freifunk_BNO=/luci-static/freifunk-bno
+	set luci.main.mediaurlbase=/luci-static/freifunk-bno
         commit luci
 EOF
-	

themes/luci-theme-freifunk-generic/root/etc/uci-defaults/luci-theme-freifunk-generic

@@ -1,4 +1,5 @@
 uci batch <<-EOF
-        set luci.themes.Freifunk_Generic=/luci-static/freifunk-generic
+	set luci.themes.Freifunk_Generic=/luci-static/freifunk-generic
+	set luci.main.mediaurlbase=/luci-static/freifunk-generic
         commit luci
 EOF

themes/luci-theme-openwrt/root/etc/uci-defaults/luci-theme-openwrt

@@ -1,6 +1,6 @@
 #!/bin/sh
 uci batch <<-EOF
 	set luci.themes.OpenWrt=/luci-static/openwrt.org
+	set luci.main.mediaurlbase=/luci-static/openwrt.org
         commit luci
 EOF
-