GeoWidget: Need to be able to select track colors based on data field

**Build**

Detected in PR 365 - Dubsky fork

```
commit 361b63bc55ac4989f17f03f33165d3070c7236b2
```

**Use Case**

I've extracted the data for tracks using the following query.

```javascript
import "experimental/geo"
from(bucket: "qa")
|> range(start: -2h)
|> filter(fn: (r) => r["_measurement"] == "voieGis" )
|> geo.toRows()
|> geo.asTracks(groupBy: ["ligne"], orderBy: ["_time"])
```

This returns records with the fields `[_time,_measurement,cl, ligne, nom, st, dur, mag, lat, lon]`. The field `cl`
indicates a class rating for each track 1,2 or 3.

**Expected Behavior**

When drawing the tracks I would like to be able distinguish between each track class with a color schema. (perhaps by width as well).

With the circle geo layer it is possible to specify colors based on a colorField and value limits.

```Javascript
colorField: 'dur',
colors: [
{type: 'min', hex: '#ff8808'},
{value: 50, hex: '#ff0888'},
{type: 'max', hex: '#343aeb'},
```

I was hoping to find a similar mechanism to display different tracks.

**Actual Behavior**

It appears that colour choice is limited to the following two combinations:

_Combo A_
```javascript
randomColors: false,
...
colors: [
{type: 'min', hex: "#110088"},
{type: 'max', hex: "#ffffdd"},
],
```
In the above configuration the two track colours are defined by `min` and `max` with endpoints getting the value for `min`. They apply to all tracks regardless of any other data values.

_Combo B_
```javascript
randomColors: true,
...
colors: undefined
```
In this second configurations the base track color is based on a palette list of 7 basic colors and white. Giraffe cycles through this palette when random is selected.

```javascript
...
const DEFAULT_TRACK_PALETTE = [
{hex: 'blue'},
{hex: 'red'},
{hex: 'green'},
{hex: 'brown'},
{hex: 'black'},
{hex: 'deeppink'},
{hex: 'olive'},
]
...
```
**Comment**

It would be nice if the user could define their own palette if random colors is desired. BTW. does it make sense to keep a random option available in the production code?

It would be nice if the user could define track colour based on a data field, as is currently the case with other geo and giraffe components.

**Screenshots**

_Defined Min/Max Colours_


_Random Colours__


**Related**
Note that when the combo `randomColor: true` is used with `colors: [...]` defined React throws an exception as reported in...

#402