Update the emscripten template to allow for starting app without any html decoration

Currently all Emscripten builds produce the same sort of html output.

We've been discussing having Debug show the current view, but Release builds being full window by default.

Something like the following:

Debug:

Release:

or

Release:

Some other options would be to have it set via code. It could be done via the window settings in main.cpp, or a static call the later would keep the main.cpp non emscripten specific.

ie:

ofxEmscripten::setLayout(ofxEmscripten::Debug);
ofxEmscripten::setLayout(ofxEmscripten::Minimal);
ofxEmscripten::setLayout(ofxEmscripten::FillWindow);

( not sure if that is the correct api approach, but just to give an idea )

cc @dimitre @Jonathhhan @NickHardeman

Note: I don't think it is possible to have an emscripten app start in Full Screen, but that might be worth looking into at the same time.

Start by locating the Emscripten template and the window settings in main.cpp. Compare the current generated HTML for Debug and Release builds, then determine whether layout selection belongs in the template or an API such as ofxEmscripten::setLayout. Done means the requested layouts are selectable and the fullscreen limitation has been investigated.