devfile/parser should use the devfile/api util override and merge functions

[maysunfaisal]

Currently, devfile/parser has override functions for each devfile object ie; components, commands etc which was the implementation that was imported over from the Odo repository. Here is the implementation in devfile/parser - https://github.com/devfile/parser/blob/master/pkg/devfile/parser/devfileobj.go#L33

However, devfile/api has override and merge util funcs defined in pkg https://github.com/devfile/api/tree/master/pkg/utils/overriding

I tested out the devfile/api funcs by integrating it into devfile/parser & odo code base and it seems to work fine. We should switch to it since it is more fleshed out and takes care of all the devfile objects.