Sets outline and opacity defaults for polygon fill

[mholthausen]

This MR

• uses mapfileStyle.width (if defined) as outlineWidth
• sets default values for outlineOpacity and opacity
  • depending on mapfileStyle.color and mapfileStyle.outlineColor the corresponding opacity values (fillOpacity and outlineOpacity) are set to the defined value or a default value
• provides a new test case for polygons defined with separate styles for fill and outline values

@KaiVolland @jansule please review

[KaiVolland]

I think this will add unneeded information to the geostyler-stlye.
If you have a very simple geostyler-style symoblizer like this:

{
  "kind": "Fill",
  "color": "#0E1058"
}

… and you write it to mapfile and reread this mapfile the result will be:

{
  "kind": "Fill",
  "color": "#0E1058",
  "fillOpacity": 0, // Not sure if its 0 but this would be even wrong
  "outlineOpacity": 0 // Not sure if its 0 but this would be even wrong
}

[mholthausen]

The result will be

{
  "kind": "Fill",
  "color": "#0E1058",
  "fillOpacity": 1, // beacuse color is defined
  "outlineOpacity": 0 // beacuse there is no outlineColor defined
}

Additionally the way (writeStyle) to generate a Mapfile from geostyler-style is not implemented yet.

[jansule]

I think this will add unneeded information to the geostyler-stlye.

I think our concept of file based similarity is a little outdated. It might be better to follow a visual-similarity-approach.

There is already an issue for this (geostyler/geostyler#1444) and this should also be discussed in the next monthly (geostyler/geostyler#1451).

IMHO, this should be non-blocking for now.