Interactive custom model editor improvements

[easbar]

Continuing from graphhopper/graphhopper#2239 the following things could/should be improved:

• [x] allow negating areas using == false
• [x] check syntax for areas section (geojson)
• [x] support boolean encoded values without ==/!= true/false? This is important especially for, e.g. if: true, limit to: 100
• [x] auto-convert tabs to spaces, visualize space characters -> no longer needed since we use json now
• [ ] fix missing auto completion for e.g. road_class ==| MOTORWAY && in_berlin
• [ ] support negation operator !
• [ ] support heading penalty
• [x] enable soft wraps? disable line numbers, disable error icons in left gutter
• [ ] full screen for editor?
• [ ] show 'no suggestions' popup instead of not showing anything when there are no suggestions?
• [ ] auto-complete some values, like empty lists for speed/priority, type: Polygon/Feature, else: "" etc.
• [ ] support areas defined in server-side profiles, does this even work?
• [x] auto-complete for YAML JSON, especially speed/priority/areas/distance_influence/limit_to/multiply_by would be nice
• [x] give better feedback for hard-to-find indentation errors (maybe use match brackets api to find closing bracket) -> not as critical for JSON anymore, we use match brackets though
• [x] enable close-brackets: https://codemirror.net/demo/closebrackets.html
• [x] catch YAML JSON syntax errors that aren't caught currently, e.g. {}[].
• [ ] maybe trigger autocomplete automatically without pressing Ctrl+Space? At least in certain cases? This way maybe users not familiar with auto-complete get to know it more easily.
• [ ] probably related to above: update (or close?) auto-complete popup when user keeps typing after it was opened?
• [x] auto-complete for numeric encoded values? maybe just show a hint saying that one needs to enter a number? show "type a number" as suggestion and insert nothing when user presses enter
• [x] tweak CM 'mode' especially indentation is not useful at all, e.g. for almost all cases it does the opposite of what we want, see here: https://codemirror.net/doc/manual.html#modeapi -> not as critical for json, and we use a black font for now since the default (red) seems a bit too much
• [ ] simplify error messages (now that they are shown at their origin) ?
• [ ] maybe use tooltips to provide some documentation, e.g. for speed/priority/distance_influence
• [ ] make it easy to translate error messages? but first make them as simple as possible.
• [x] maybe use code mirror bracket matching
• [ ] adjust colors, theme and styles
• [ ] check code mirror options to see if we need anything besides the defaults, maybe customize the 'mode'?
• [x] handle YAML multiline syntax like >+ and |... https://stackoverflow.com/a/21699210 we use JSON now
• [ ] dark theme and VIM keybindings (just kidding...)

[easbar]

The font color (currently black) should be improved a bit maybe something like this:

Choosing the default json 'mode' was not so helpful, because the font was mostly red (too alarming) and the indentation did not work very well (see comment above).