Added UIApplication class to easily initialize GUI Applications.

Addind 7GUIs examples (https://eugenkiss.github.io/7guis/). Currently implemented the first three: Counter, Temperature Converter and Flight Booker.
Fixes in IgnoreMatcher and ProjectDirectoryTree.
Window::runMainLoop now accepts an std::function<void()>, this allows to use lambdas with captures.
UITextInput when using only numbers allow to insert + and - at the beggining of the number.
Return Node* on Node::setFocus().
String::fromFloat and String::fromDouble will shrink the number as much as possible (delete extra 0 and .).

bin/assets/ui/breeze.css

@@ -185,7 +185,8 @@ SelectButton:selected:pressed {
 }
 
 pushbutton:disabled,
-selectbutton:disabled {
+selectbutton:disabled,
+textinput:disabled {
 	color: var(--disabled-color);
 	border-color: var(--disabled-border);
 }