supress visibility of unclaimed tips (issue #146)

* filtered all Tips relations through the Tips:with_address scope
      except for UsersController#show (private page)
* filtered users with zero withdrawn_amount in UsersController#index
* removed :no_bitcoin_address message from Tips#index

NOTES:

i do not have a full setup (blockchain account , etc) so i could not test this feature manually - it was implemented driven by cucumber tests which are not included in this PR because they were implemented on the tip of my HEAD using an incompatible routing/testing scheme implemented in PR #141 and would cause travis to fail today - they are included in PR #142 along with tests for several other recent features pending merge of the new pretty url routing scheme

regarding the TipsController#index action switched on no params -
  # the original query
  Tip.includes(:user , :project)
  # the replacement query
  Tip.with_address.includes(:project)
the Tips:with_address scope joins(:user) so this should not have broken anything but unfortunately no tests exist for the Tips view so this should be verified manually on a staging system

rearding the UsersController#index action -
im a bit uncertain of the semantics here but the User :withdrawn_amount is based on the tips.paid scope which is based on the existence of a :sendmany_id - so im assuming that this means that a tip that was offered to someone without bitcoin_address would not have a sendmany_id and any so such user would have a zero withdrawn_amount