Expose exoplanet creation settings to user as module properties (#1499)

* Expose exoplanet creation settings to user as module properties

* Set default textures from asset to avoid explicit paths to sync folder

data/assets/scene/milkyway/exoplanets/exoplanets_data.asset

@@ -4,6 +4,14 @@ local DataPath = asset.syncedResource({
     Identifier = "exoplanets_data",
     Version = 2
 })
+
+asset.onInitialize(function () 
+    local p = "Modules.Exoplanets.DataFolder";
+    if(openspace.getPropertyValue(p) == "") then
+        openspace.setPropertyValueSingle(p, DataPath)
+    end
+end)
+
 asset.export("DataPath", DataPath)
 
 asset.meta = {

data/assets/scene/milkyway/exoplanets/exoplanets_textures.asset

@@ -1,4 +1,5 @@
-asset.require('./../habitable_zones/habitable_zone_textures')
+local habitableZoneTextures =
+    asset.require('./../habitable_zones/habitable_zone_textures').TexturesPath
 
 local TexturesPath = asset.syncedResource({
     Name = "Exoplanet Textures",
@@ -6,6 +7,37 @@ local TexturesPath = asset.syncedResource({
     Identifier = "exoplanets_textures",
     Version = 2
 })
+
+asset.onInitialize(function ()
+    local starTexture = TexturesPath .. "/sun.jpg"
+    local noDataTexture = TexturesPath .. "/grid-32.png"
+    local discTexture = TexturesPath .. "/disc_bw_texture.png"
+
+    local hzTexture = habitableZoneTextures .. "/hot_to_cold_faded.png"
+
+    -- Set the default textures used for the exoplanet system creation
+    -- (Check if already set, to not override value in config file)
+    local p = "Modules.Exoplanets.StarTexture";
+    if(openspace.getPropertyValue(p) == "") then
+        openspace.setPropertyValueSingle(p, starTexture)
+    end
+
+    p = "Modules.Exoplanets.NoDataTexture";
+    if(openspace.getPropertyValue(p) == "") then
+        openspace.setPropertyValueSingle(p, noDataTexture)
+    end
+
+    p = "Modules.Exoplanets.OrbitDiscTexture";
+    if(openspace.getPropertyValue(p) == "") then
+        openspace.setPropertyValueSingle(p, discTexture)
+    end
+
+    p = "Modules.Exoplanets.HabitableZoneTexture";
+    if(openspace.getPropertyValue(p) == "") then
+        openspace.setPropertyValueSingle(p, hzTexture)
+    end
+end)
+
 asset.export("TexturesPath", TexturesPath)
 
 asset.meta = {