/issues/new improvements for plotting area/route and error handling

This problem arose as I didn't spot the "Draw an Area" text when I was trying to draw a route - could the currently selected mode (area/route/point) be highlighted? Ideally the mode's icon would become coloured, eg green, but at the very least the text underneath the icon should stay green once selected - currently it's only green during mouseover.

Less importantly, I'd also prefer 'route' as the default initial option, and think the "Drag the grey points to create new corners." text should appear in area- as well as route-mode. Arguably when in route mode it should be "Drag the grey points to create new points."

When in area-mode I could double-click on the second point - this would be apt for routes but it allows a line to be drawn when in area mode, leading to a non-intuitive error message of: "Provide a location can't be blank" - I had provided a location, but it was an empty area rather than the straight line I'd intended.

Then when the page reloads, data entered in sections 1 and 5 is retained, but sections 2 (photo) and 4 (tags) are cleared so data must be re-entered. I don't know about sections 6 and 7 as I wasn't using them, but having to re-enter the data in sections 2 and 4 was frustrating, as was the problem with section 3 (location) which didn't make sense until I worked out the system was allowing me to submit an empty area then describing it as blank rather than empty.

Start at the /issues/new form and reproduce the area, route, and point drawing flows, including submission errors and page reloads. Done means the selected mode is visibly indicated, the relevant guidance and default mode are correct, invalid empty areas produce an understandable error, and entered data is retained after reload.