Reorganise branches to move temporary work branches into a separate top level area

Currently the top level svn 'branches' folder is used for temporary branches, when working on particular big feaures, ODE forks, and release branches.

To avoid this folder becoming too overloaded, the temporary work branches will be moved out to a top level 'workspace' folder, leaving the branches folder just for the ODE fork (ODE-1.x-fixes) and the release branches. These are permanent branches that need to be maintained, whereas the branches in the 'workspace' will be temporary and can therefore be removed when no longer required.