Support custom layout-screen-size-threshold in mdl-layout

[mscudlik]

Please add the support for a custom screen size treshhold in mdl-layout.
Currently i can change the sass variable layout-screen-size-threshold to my desired value, but in the layout component a hard coded value is used to detect if a small screen is used. see sass variable here and hard coded value here
Changing only layout-screen-size-threshold leads to a mobile layout where the layout-drawer is still shown.

Using bootstrap4 for example, 768px is used as a treshhold/breakpoint and you cannot get a common look and feel this way.

Thanks a lot for your great work and best regards,
Matthias

[mseemann]

will works as follow:

/ * The LAYOUT_SCREEN_SIZE_THRESHOLD can be changed at the root module. Just provide a value for this OpaqueToken:
 *
 * providers: [
 *  {provide:LAYOUT_SCREEN_SIZE_THRESHOLD, useValue: 768 }
 * ]
 *
 * you also need to change the scss variable to the same value: $layout-screen-size-threshold: 768px.
*/
export const LAYOUT_SCREEN_SIZE_THRESHOLD = new OpaqueToken('layoutScreenSizeThreshold');