Generate the gresource xml file based on a list of resources

This inverts the logic from
- having an xml file and extracting dependencies
  from it to
- having a list of dependencies and generating
  an xml file from it

In the original configuration adding or removing a
resource to/from the gresources.xml file would not
be detected by cmake as a change in dependencies.
The user would have to remember to rerun cmake manually.
By explicitly listing the dependencies, cmake will
properly recongifure and regenerate if that list is
updated. The remainder of the dependency configuration
also ensures proper rebuilds of gnucash, libaqbanking
and libofx if any of the resource files change, a new
one is added or an existing one is removed.

For reusability the code to generate the gresource related
files as been extracted into a separate function.

CMakeLists.txt

@@ -39,6 +39,7 @@ include (CheckIncludeFiles)
 include (GncAddSchemeTargets)
 include (GncAddGSchemaTargets)
 include (GncAddTest)
+include (GncGenerateGResources)
 include (MakeDistFiles)
 include (GNUInstallDirs)
 include (TestBigEndian)