make the parse function more generic

[yangcao77]

devfile/libray currently has 4 parse functions ParseFromPath, ParseFromURL, ParseFromData, ParseRawDevfile
The logic of those 4 parse functions are similar, the only difference is that they take different parameter types.

The issue is to deprecate the existing parse functions, and create a new ParseDevfile, which combines the logic of those 4 functions. It should take an argument as following:

type ParserArgs struct {
	path             string
	url              string
	data             []byte
	flattenedDevfile *bool	// default to true
	registryURLs     []string
}

Populate() and PopulateFromURL() and PopulateFromRaw() should also be combined.