Add Thunderforest map layers

Also drop the 8-bit Google layer which just shows the default
Google map layer nowadays and add header comments before
grouped layer definitions.

data/default_configuration_files/map_config.conf

@@ -1,6 +1,6 @@
 ## this config file configures the available map layers
 
-revision=20 ## configuration file revision
+revision=21 ## configuration file revision
 
 ## new layers use OSM style coordinates by default
 
@@ -26,6 +26,8 @@ revision=20 ## configuration file revision
 ## Layers section
 [layers]
 
+## OpenStreetMap layers
+
 [[mapnik]]
   label=OSM Mapnik (default)
   url="http://c.tile.openstreetmap.org/"
@@ -163,6 +165,8 @@ revision=20 ## configuration file revision
 #  folder_prefix=OpenStreetMap II
 #  coordinates=osm
 
+## Stamen Design
+
 [[stamen_toner]]
   label=Toner
   url="http://tile.stamen.com/toner/"
@@ -193,6 +197,50 @@ revision=20 ## configuration file revision
   coordinates=osm
   group="stamen"
 
+## Thunderforest
+
+[[thunderforest_transport]]
+  label=Transport
+  url="http://tile.thunderforest.com/transport/"
+  type=png
+  max_zoom=18
+  min_zoom=0
+  folder_prefix=thunderforest_transport
+  coordinates=osm
+  group="thunderforest"
+
+[[thunderforest_transport_dark]]
+  label=Transport Dark
+  url="http://tile.thunderforest.com/transport-dark/"
+  type=png
+  max_zoom=18
+  min_zoom=0
+  folder_prefix=thunderforest_transport_dark
+  coordinates=osm
+  group="thunderforest"
+
+[[thunderforest_landscape]]
+  label=Landscape
+  url="http://tile.thunderforest.com/landscape/"
+  type=png
+  max_zoom=18
+  min_zoom=0
+  folder_prefix=thunderforest_landscape
+  coordinates=osm
+  group="thunderforest"
+
+[[thunderforest_outdoors]]
+  label=Outdoors
+  url="http://tile.thunderforest.com/outdoors/"
+  type=png
+  max_zoom=18
+  min_zoom=0
+  folder_prefix=thunderforest_outdoors
+  coordinates=osm
+  group="thunderforest"
+
+## Google
+
 [[gmap]]
   label=Google maps
   url="http://mt1.google.com/vt/"
@@ -313,15 +361,7 @@ revision=20 ## configuration file revision
   group="google"
   timeout=12
 
-[[g8bit]]
-  label=Google 8-bit
-  url="http://mt1.google.com/vt/lyrs=8bit,m"
-  type=png
-  max_zoom=21
-  min_zoom=0
-  folder_prefix=Google 8-bit
-  coordinates=google
-  group="google"
+## Virtual Earth
 
 [[vmap]]
   label=Virtual Earth-map
@@ -363,6 +403,8 @@ revision=20 ## configuration file revision
   coordinates=quadtree_substitution
   group="virtual_earth"
 
+## Yahoo
+
 [[ymap]]
   label=Yahoo map
   url=http://maps.yimg.com/hx/tl?&s=256
@@ -398,6 +440,8 @@ revision=20 ## configuration file revision
   coordinates=yahoo
   group="yahoo"
 
+## Czech Republic related layers
+
 [[cz_mtb]]
   label=Europe MTB
   url="http://tile.mtbmap.cz/mtbmap_tiles/"
@@ -408,11 +452,11 @@ revision=20 ## configuration file revision
   coordinates=osm
   group=cz
 
-# Freemap.sk
-# NOTE: type=jpeg - upper levels use PNG and lower JPG
-# so the resulting file extension (if used) might not be correct
-# - this shouldn't be problem, as modRana uses magic numbers,
-# not file extension when loading tiles from storage
+## Freemap.sk
+## NOTE: type=jpeg - upper levels use PNG and lower JPG
+## so the resulting file extension (if used) might not be correct
+## - this shouldn't be problem, as modRana uses magic numbers,
+##   not file extension when loading tiles from storage
 
 [[freemap_sk_autoatlas]]
   label=FM.sk autoatlas
@@ -474,6 +518,8 @@ revision=20 ## configuration file revision
   coordinates=web_mercator_substitution
   group="cz"
 
+## Special map layers
+
 [[submarine_cable_map]]
   label=Submarine Cable Map
   url="http://b.tiles.telegeography.com/maps/submarine-cable-map-2013/"
@@ -484,6 +530,8 @@ revision=20 ## configuration file revision
   coordinates=osm
   group="special"
 
+## European map layers
+
 [[map1_eu]]
   label=map1.eu
   url="http://beta.map1.eu/tiles/"
@@ -627,6 +675,9 @@ revision=20 ## configuration file revision
 [[stamen]]
   label="Stamen design"
 
+[[thunderforest]]
+  label="Thunderforest"
+
 [[google]]
   label="Google"