[2.x] Dashboard customisable line width.

__Use case:__
The lines in the graphs and other dashboard elements are too thin. It's hard to see the lines from a distance (for instance when you put them on a big screen as a dashboard).

__Proposal:__
Editable line width. Also it would be great to be able to further customize width and look of other dashboard elements.

__Current behaviour:__
It's not possible to edit line width for the graphs.

__Desired behaviour:__
Customisable line width etc.

__Alternatives considered:__
Using grafana instead as it supports more customisation on graphical elements.
Thing is that I like how influx DB UI looks, it's almost at a point where it can replace grafana completely for me.

The issue names no files, tests, or entry points. Start by locating the dashboard graph visualization UI; define the line-width control and its scope, then verify that dashboard graphs visibly honor the setting.

Written by the indexing model from the issue text.