Add SD theme system

Adds installable SD-card themes with manifest downloads, theme registry parsing, themed home/chrome/settings/file browser support, FreeInk layout integration, theme documentation, and layout tests.

src/activities/settings/SettingsActivity.h

@@ -23,6 +23,7 @@ enum class SettingAction {
   SdFirmwareUpdate,
   Language,
   DownloadFonts,
+  DownloadThemes,
 };
 
 struct SettingInfo {
@@ -166,6 +167,7 @@ class SettingsActivity final : public Activity {
   void toggleCurrentSetting();
   void openSleepTimeoutPicker();
   void rebuildSettingsLists();
+  void releaseSettingsLists();
   void syncQuickResumeTimeoutForSleepScreen(bool sleepScreenChanged, bool quickResumeTimeoutChanged);
 
  public: