Allow contributors to add points of interest

[ZeLonewolf]

This PR sets up the structure for contributors to add POI icons with the following scheme:

• POI icons are black PNGs that are recolored in the style
• All POIs are contained in a single style layer with selectors to set color, icon, etc

As a demonstrar, this PR includes bars/pubs and hospitals to show how the single selector works. In addition, the source SVGs for the icons are included.

Eventually I'd like to be able to produce the PNGs from SVG at compile time so contributors can deal solely with SVGs.

The initial icons and colors are not great thanks to my limited design skills. Improvements welcome :)

[1ec5]

We should continue the discussion in #128 about whether we should minimize the number of POI icon colors, as we’ve done with roads, or have POIs occupy the full color spectrum.

[ZeLonewolf]

I've updated this PR based on feedback received. Some screen shots:

Location: (localhost link)

Location: (localhost link)

Location: (localhost linkl)

[1ec5]

Do we need anything in the way of documentation? For example, the contributor’s guide could explain the POI color categories and lay out some initial criteria for POI classes at each zoom level.

[ZeLonewolf]

@1ec5 :
Normalizing icon sizes:

[ZeLonewolf]

Do we need anything in the way of documentation? For example, the contributor’s guide could explain the POI color categories and lay out some initial criteria for POI classes at each zoom level.

Yes, will work on adding that.

[zekefarwell]

This is looking good. I like the hospital icon, but I find the cross icon for other medical facilities looks inconsistent with it. I think changing the cross to white inside a blue round rect would unify both icons as the same general category.

[ZeLonewolf]

Blowing the dust off this PR. Current state:

I see that @zekefarwell made a suggestion to make the cross icon consistent with the hospital "H" icon, so I'm planning to experiment with that next.

[ZeLonewolf]

I added a bunch of text to the contributing guide, so this section is no longer on the "bottom"

[ZeLonewolf]

Updated screen shot:

[1ec5]

We’ve come a long way since June. The selection of POI types is rather absurdly minimalistic, but let’s get this layer into users’ hands to give a sense of what’s possible and iterate further in separate PRs.

[ZeLonewolf]

[ZeLonewolf]