shell.py: Added transaction import

Since we use the ZopeTransactionThingy we have to use the transaction
module to commit() our changes
Merge pull request #56 from Turbo87/shell-transaction

shell.py: Added transaction import
templates/base-page: Added header_tabs option
templates/ranking: Use header tabs instead of pills
templates/pager: Fixed format
controllers/ranking: Move year parsing out of __get_result() method
lib/helpers: Export dict() and min/max() functions

These should exist in Jinja2, but somehow they don't...
templates/pager: Allow custom URL parameters aside from the page
templates/ranking: Pass year parameter to pager
templates/ranking: Added basic years dropdown
templates/ranking: Added year parameter to header tabs links
controllers/ranking: Merged duplicate code
templates/ranking: Removed hardcoded year list
controllers/ranking: Make the current year the default
Merge pull request #57 from Turbo87/rankings

Rankings with season filter
Merge branch 'master' into search