make title optional
make title optional

this fixes a problem identified in #859
<<view server.bag spaceLink>>
should generate a space link to the space identified by the server.bag field
no title is provided in this situation thus it is currently broken

TODO: I looked at porting the existing tests from
http://svn.tiddlywiki.org/Trunk/contributors/PaulDowney/plugins/TiddlySpaceLinkPlugin/test/
to minimise these sorts of problems
however these require porting the TiddlyWiki wikifier code.
either need to do this or rewrite the tests

FND/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace,FND/tiddlyspace