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/ActivityManager.cpp

@@ -9,6 +9,7 @@
 #include "boot_sleep/BootActivity.h"
 #include "boot_sleep/SleepActivity.h"
 #include "browser/OpdsBookBrowserActivity.h"
+#include "components/UITheme.h"
 #include "home/CrashActivity.h"
 #include "home/FileBrowserActivity.h"
 #include "home/HomeActivity.h"
@@ -170,6 +171,7 @@ void ActivityManager::replaceActivity(std::unique_ptr<Activity>&& newActivity) {
 }
 
 void ActivityManager::goToFileTransfer() {
+  UITheme::getInstance().releaseSdThemeAssetMemory();
   replaceActivity(std::make_unique<CrossPointWebServerActivity>(renderer, mappedInput));
 }
 
@@ -184,6 +186,7 @@ void ActivityManager::goToRecentBooks() {
 }
 
 void ActivityManager::goToBrowser() {
+  UITheme::getInstance().releaseSdThemeAssetMemory();
   const auto& servers = OPDS_STORE.getServers();
   // Skip the server picker when there's only one server configured
   if (servers.size() == 1) {
@@ -194,6 +197,7 @@ void ActivityManager::goToBrowser() {
 }
 
 void ActivityManager::goToReader(std::string path) {
+  UITheme::getInstance().releaseSdThemeAssetMemory();
   replaceActivity(std::make_unique<ReaderActivity>(renderer, mappedInput, std::move(path)));
 }
 
@@ -223,6 +227,7 @@ void ActivityManager::goHome(HomeMenuItem initialMenuItem) {
       initialMenuItem = HomeMenuItem::SETTINGS_MENU;
     }
   }
+  UITheme::getInstance().reload();
   replaceActivity(std::make_unique<HomeActivity>(renderer, mappedInput, initialMenuItem));
 }
 void ActivityManager::goToCrashReport() { replaceActivity(std::make_unique<CrashActivity>(renderer, mappedInput)); }