Perform initial refactoring work

Things that were once singletons are no longer singletons, but are
instead stored in the "Application" singleton

Some singletons still remain, and some renaming/renamespacing is left

src/singletons/accountmanager.hpp

@@ -7,10 +7,11 @@ namespace singletons {
 
 class AccountManager
 {
-    AccountManager();
+    AccountManager() = default;
+    friend class Application;
 
 public:
-    static AccountManager &getInstance();
+    ~AccountManager() = delete;
 
     void load();