[#5973] remove pysvn dependency from Allura package
[#5973] Contextual reminder if setup-app was not run
[#5973] don't install ForgeActivity app if it's not enabled
[#5973] rename rebuild.bash to rebuild-all.bash with more helpfulness
[#5973] Make the pysvn dep explicit, so we fail sooner (setup.py develop instead of runtime import)
[#5973] remove ancient README within the Allura dir since we have a top-level one
[#5973] Simplify the README

* explain SVN is optional (often tricky to install on some platforms)
* use rebuild-all.bash
* omit SCM symlinks since they don't add anything useful (/tmp works just fine for getting started)