Fix remaining typechecks in gmf

[adube]

This patch fixes the remaining type issues in GMF.

Following @fredj recommendation, I copied the properties from ("ngeo/datasource/OGC.js").OGCOptions to ("gmf/datasource/OGC.js").OGCOptions, because typescript doesn't currently support inheritence of objects for typing purpose.

There are also 2 remaining errors that I don't know what to do about. They are about the use of DocumentTouch property, which seems to be deprecated. I suspect this is something that needs to be addressed (and not just ignored using ts-ignore). Here they are:

contribs/gmf/src/controllers/bootstrap.js:24:65 - error TS2339: Property 'DocumentTouch' does not exist on type 'never'.

24       if (small_screen && (('ontouchstart' in window) || window.DocumentTouch && document instanceof DocumentTouch)) {
                                                                   ~~~~~~~~~~~~~

contribs/gmf/src/controllers/bootstrap.js:24:102 - error TS2304: Cannot find name 'DocumentTouch'.

24       if (small_screen && (('ontouchstart' in window) || window.DocumentTouch && document instanceof DocumentTouch)) {
         

[fredj]

See #4609 for the DocumentTouch warning

[adube]

All done. Ready merge?

[sbrunner]

Merge when Travis is OK :-)