generate comment text for cross-border regions

* without references to national contexts for the moment, as this
  needs to rely on different source data format
fixed route for browsehappy action
* moved current year display to top of map, removed year references in city info growth rate text
* hide SVG elements initially, to avoid mega white space on bottom part of page
removed colophon text from footer, added some padding before footer
de-startuppify beta sticker
updated missing data text for commentary texts

* from "No data available for <CITY> in <YYYY>" to
  "No data available for <COUNTRY> until <first_year_of_data>"
* this will break for transborder MRs with current CSV data, but
  missing data at beginning of time series does not involve countries
  with transborder MRs so all is fine for the time being
compose and display y axis label in line charts
copy fix
let lis breathe
rearranged content in static and interactive sections
backported tiles layout from lsecities.net
added explanations of legends interaction (click, double-click)