Add PMTiles support (#938)

Add support for pmtiles sources. Solves #807 

<strike>
There is still an error, probably when adding the source to the Maputnik
sources:

```
Failed to process sources for 'pmtiles://https://example.com/data/switzerland.pmtiles' TypeError: NetworkError when attempting to fetch resource.
    fetchSources App.tsx:642
```

@bdon How did you solve this for https://editor.protomaps.com/ ?
</strike>

---------

Co-authored-by: Brandon Liu <bdon@bdon.org>
Co-authored-by: WebFreak001 <gh@webfreak.org>
Co-authored-by: ShellyDCMS <60476837+ShellyDCMS@users.noreply.github.com>
Co-authored-by: Harel M <harel.mazor@gmail.com>

src/components/ModalSources.tsx

@@ -51,6 +51,7 @@ function editorMode(source: SourceSpecification) {
   }
   if(source.type === 'vector') {
     if(source.tiles) return 'tile_vector'
+    if(source.url && source.url.startsWith("pmtiles://")) return 'pmtiles_vector'
     return 'tilejson_vector'
   }
   if(source.type === 'geojson') {
@@ -129,6 +130,10 @@ class AddSource extends React.Component<AddSourceProps, AddSourceState> {
     const {protocol} = window.location;
 
     switch(mode) {
+    case 'pmtiles_vector': return {
+      type: 'vector',
+      url: `${protocol}//localhost:3000/file.pmtiles`
+    }
     case 'geojson_url': return {
       type: 'geojson',
       data: `${protocol}//localhost:3000/geojson.json`
@@ -240,6 +245,7 @@ class AddSource extends React.Component<AddSourceProps, AddSourceState> {
           ['tile_raster', t('Raster (Tile URLs)')],
           ['tilejson_raster-dem', t('Raster DEM (TileJSON URL)')],
           ['tilexyz_raster-dem', t('Raster DEM (XYZ URLs)')],
+          ['pmtiles_vector', t('Vector (PMTiles)')],
           ['image', t('Image')],
           ['video', t('Video')],
         ]}