Cleans up command_line_options.h

Query methods are not accessor functions. So use camel-case names for them.
Cleans up desktop_file.h

Query methods are not accessor functions. So use camel-case names for them.
Cleans up file_search_service.h

Query methods are not accessor functions.
Command methods are not mutator functions.
So use camel-case names for them.
Cleans up icon_service.h

Command methods are not mutator functions. So use camel-case names for them.
Public methods come before private methods.
Cleans up menu.h

Command methods are not mutator functions.
Query methods are not accessor functions.
So use camel-case names for them.

Renames type names and function names to be in camel case (Google style guide)

Public methods come before private methods.
Cleans up messages.h

Uses camel case for function names (Google style guide)
Cleans up subcategory.h

Query methods are not accessor functions.
So use camel-case names for them.
Cleans up representation.h - first cut

Use interface class when meant