improve molecular-profile-select field's prompt(s)

[jmcmichael]

Currently, mp-select initially displays the prompt 'Select a Gene and Variant to specify a simple Molecular Profile', which doesn't mention complex MPs. It should be rewritten to include a hint on how to find/add complex MPs in addition to the simple Gene/Variant selection method.

Additionally, this prompt remains even if the MP Editor is displayed, which may be confusing. Ideally it should be hidden when the Editor is displayed, or its text updated to make sense with the editor shown or hidden.