UI: Upgrade stream link hotlink to a button

Most of the top streaming services now have a link in the stream key
label. Upgrading this button to a button clarifies the assistance
for the important step of setting up a stream.

Creates a new type of button for URL opening simply which also
automatically updates the tootip to the current URL.

Includes addition of Twitter/Periscope URL to make this feature more
complete.

UI/CMakeLists.txt

@@ -243,6 +243,7 @@ set(obs_SOURCES
 	combobox-ignorewheel.cpp
 	spinbox-ignorewheel.cpp
 	record-button.cpp
+	url-push-button.cpp
 	volume-control.cpp
 	adv-audio-control.cpp
 	item-widget-helpers.cpp
@@ -298,6 +299,7 @@ set(obs_HEADERS
 	menu-button.hpp
 	mute-checkbox.hpp
 	record-button.hpp
+	url-push-button.hpp
 	volume-control.hpp
 	adv-audio-control.hpp
 	item-widget-helpers.hpp