iOS port initial commit

Known Issues
------------
- No printing support.
- No typing support using the OS virtual keyboard.  iOS needs to be signalled
  to bring up the virtual keyboard when the text tool is active.  We also may
  need to do some finagling to make IM work with the virtual keyboard.
- OS language detection doesn't work yet.
- Quitting doesn't close the app.  It just displays a black screen until it is
  force-closed.
- Need to include cross-compilation instructions.

Possible Issues
---------------
- No text display.  This is likely an issue with how pango and related
  libraries were cross-compiled rather than an issue with Tux Paint code.  From
  the error output it appears to be a font rendering issue.
- SVG integration couldn't be tested because RSVG library has not yet be
  cross-compiled successfully.
- Only tested under the iOS Simulator (and not on an actual iOS device yet.)

ios/Info.plist

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>English</string>
+	<key>CFBundleExecutable</key>
+	<string>tuxpaint</string>
+	<key>CFBundleGetInfoString</key>
+	<string>0.9.26, Copyright 2009-2020, Tux Paint Development Team</string>
+	<key>CFBundleIconFile</key>
+	<string>tuxpaint.icns</string>
+	<key>CFBundleIdentifier</key>
+	<string>com.newbreedsoftware.tuxpaint</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>Tux Paint</string>
+	<key>CFBundlePackageType</key>
+	<string>APPL</string>
+	<key>CFBundleShortVersionString</key>
+	<string>0.9.26</string>
+	<key>CFBundleSignature</key>
+	<string>TXPT</string>
+	<key>CFBundleVersion</key>
+	<string>2020-12-27</string>
+    <key>UISupportedInterfaceOrientations</key>
+    <array>
+        <string>UIInterfaceOrientationLandscapeLeft</string>
+        <string>UIInterfaceOrientationLandscapeRight</string>
+    </array>
+    <key>UIStatusBarHidden</key>
+    <true/>
+    <key>UIViewControllerBasedStatusBarAppearance</key>
+    <false/>
+    <key>UILaunchStoryboardName</key>
+    <string>Splash</string>
+</dict>
+</plist>