Make "base" landuse colours more consistent

"Base" landuse colours have some issues and are generally without a great deal of reason. As some examples

* Lightness is all over the place
* Of the "base" landuses only ``landuse=retail`` has a border, but it's strong-red, only it's got a width of 0.3 so you don't realize it.
* ``landuse=retail`` is more closely related to shop POIs than ``landuse=commercial``, but ``landuse=commercial`` has a colour more similar to the shop colours

A few things are done here

* Split out "base" solid landuse colours of residential, retail, commercial, industrial/railway, and farm/farmland.
* Gives them all the same lightness of 89. This is about the same as residential and retail were, and lightens the others, particularly commercial and industrial.
  * This basically flips retail and commercial in some ways. I looked at keeping them more the same, but I kept on tending to this, so decided to do it this way so that there was a colour difference between them
* Adjusts chromas
* Moves the industrial hue farther away from red. This is necessary with such light colours to allow it to be distinct from commercial while commercial is distinct from both retail and residential.
* Adds light lines to the ones missing them, consistent with current retail, school/university/college/hospital/kindergarten and most more POI-like landcover styles
  * Retail centres, industrial parks, residential development and commercial areas may all be named, and with a name is useful to have a border to indicate what size area the name applies to.
  * It aids in showing the limits between railway usage and adjacent industrial usage
  * Farm fields can be individually mapped, and the lines can be useful there, and those areas are typically low-clutter
  * The effect is intentionally fairly subtle
* Widened existing lines around retail, but still under 1 pixel. This helps with antialiasing artefacts. I didn't go all the way to 1, because I found that looked worse where there were two adjacent landuses of the same type.

It is possible to compute the difference between colours, either by transforming to Luv and using Euclidean distance, or [calculating directly in Lch](https://en.wikipedia.org/wiki/LCH_color_space#Color_and_hue_difference)

```
         Res.  Retail  Comm.  Ind.   Farml.
Farml.   12.0    12.4   10.0  17.3      0
Ind.      9.0    13.9    8.1   0
Comm.     8.5    7.6     0
Retail   16.0    0
Res.      0
```
Rework farmyard colour

Although not quite a "base" landuse in the same way farmland is, it's
worth handling at the same time to keep it in harmony with farmland.
Make base landuse lines slightly narrower for unnamed landuses
Split apart railway and industrial landuse explicitly

Carto did this before when preprocessing, but doing it explicitly makes it easier to make later changes to one but not the other
Don't use outlines for unnamed railway landuse

Railway landuse can span wide areas and sometimes needs to be broken up at
arbitrary places, similar to rivers.

Faint outlines are maintained on named railway landuse, which is typically yards
Add colour variable for landuse_railway

This makes customization easier and makes it clear that it's intentional
that it's the same colour as industrial.

The same is not done for farm/farmland because it is unlikely that anyone would want to differentiate between those two tags as they mean the same thing.
Merge branch 'pnorman-landcover_recolour'