Provide properties pages with resource selection dialogs

[gerking]

The LaTeX properties page requires users to manually type in the names of certain files or folders. This is really cumbersome because users need to memorize the precise names before opening the properties. Instead, provide some mechanism to choose between existing resources below the project root. Possible solutions are summarized here: https://wiki.eclipse.org/FAQ_How_do_I_prompt_the_user_to_select_a_resource%3F