Fixes and Improvements for web view of a lightning node

this pull request contain the following fixes:

Docker build fix. (python 3.7 is needed to build correct)
fixed link to view the highest bitcoin block at the blockchain. (smartbit is down)
fixed the fee calculation on the event list. (millisat fees where always round down)
fixed the map view. (it is an memory overflow in your local browser, which kills the application. i filtered the view to only the nodes connected with your node with channels between them and you. this is i think also a nice view, how your node is connected. :) )

djmelik / lndash