themes need to @import bootstrap{,/variables}, so they can override

(in preparation for upcoming cider theme)
haml: remove whitespace from inside .label
views: workspace/executions: remove tr.spacer from table
sass: small visual fixes
sass: make colors_and_states themeable
rails env: Set Haml output to ugly everywhere
haml: add partial 'semantic_version'
ui: navbar: show version next to brand IF it's a pre-release