First stage of options rework.

First stage of options rework.

- Split Configuration into RCConfiguration and SessionConfiguration;
the first for options which are saved to .rc files and the second
for options which are saved in a session file.

- Move some options from the old `master' Configuration object into
SessionConfiguration; this needs more refinement.

- Reflect many RCConfiguration options in an expanded Edit->Preferences
dialog; my intention is to remove the corresponding menu items
eventually.

git-svn-id: svn://localhost/ardour2/branches/3.0@5075 d708f5d6-7413-0410-9779-e7cbd77b26cf