Add RTL level property and print flag

Again, the RTL property controls whether textboxes will be
right-aligned, and that kind of stuff. It can't be font-bound, since
Space Station supports Hebrew characters and we want to be able to
support, say, a Hebrew translation or Hebrew levels in the future
without having to make a dedicated (or duplicated) font for it.
Therefore it's a property of both the language pack as well as custom
levels - like custom levels already had a <font> tag, they now also
have an <rtl> tag that sets this property.

Right now, we'll have to hardcode it so the menu option for the Arabic
font sets the <rtl> property to 1, and all the other options set it to
0. But it's future-proof in that we can later decide to split the
option for Space Station into an LTR option and an RTL option (so both
"english/..." and "עברית" would select Space Station, but one sets the
RTL property to 0 and the other sets it to 1).

desktop_version/src/CustomLevels.cpp

@@ -227,6 +227,7 @@ TAG_FINDER(find_desc2, "Desc2")
 TAG_FINDER(find_desc3, "Desc3")
 TAG_FINDER(find_website, "website")
 TAG_FINDER(find_font, "font")
+TAG_FINDER(find_rtl, "rtl")
 
 /* For CliPlaytestArgs */
 TAG_FINDER(find_playtest, "Playtest")
@@ -315,6 +316,7 @@ bool customlevelclass::getLevelMetaDataAndPlaytestArgs(const std::string& _path,
     {
         _data.level_main_font_idx = font::get_font_idx_8x8();
     }
+    _data.rtl = help.Int(find_rtl(buf).c_str());
 
 
     if (pt_args != NULL)
@@ -1037,6 +1039,7 @@ bool customlevelclass::load(std::string _path)
 
     version = 0;
     level_font_name = "font";
+    rtl = false;
 
     for (pElem = hDoc
         .FirstChildElement()
@@ -1104,6 +1107,11 @@ bool customlevelclass::load(std::string _path)
                 {
                     level_font_name = pText_;
                 }
+
+                if(SDL_strcmp(pKey_, "rtl") == 0)
+                {
+                    rtl = help.Int(pText_);
+                }
             }
         }
 
@@ -1524,6 +1532,20 @@ bool customlevelclass::save(const std::string& _path)
         }
     }
 
+    if (rtl)
+    {
+        xml::update_tag(msg, "rtl", rtl);
+    }
+    else
+    {
+        // Also get rid of this one...
+        tinyxml2::XMLElement* element;
+        while ((element = msg->FirstChildElement("rtl")) != NULL)
+        {
+            doc.DeleteNode(element);
+        }
+    }
+
     xml::update_tag(data, "mapwidth", mapwidth);
 
     xml::update_tag(data, "mapheight", mapheight);