Change ScreenManager to no longer reuse screen instances.

[crykn]

Change ScreenManager to no longer reuse screen instances. This leads to closer resemblence with libGDX's Game class.

To test these changes, use version c9a1f42d83 for screenmanager and version v0.3.5 for guacamole. The GWT extension was removed, so the GWT dependencies should now look like this:

implementation "com.github.crykn.guacamole:core:$guacamoleVersion:sources"
implementation "com.github.crykn.guacamole:gdx:$guacamoleVersion:sources"
implementation "com.github.crykn.guacamole:gdx-gwt:$guacamoleVersion"
implementation "com.github.crykn.guacamole:gdx-gwt:$guacamoleVersion:sources"
implementation "com.github.crykn:libgdx-screenmanager:$screenManagerVersion:sources"
implementation "com.github.tommyettinger:formic:$formicVersion:sources"

The module file needs to include the following entry:

<inherits name="libgdx_screenmanager" />

Changes

• Screens & transitions don't have to be registered anymore; ScreenManager#push now takes a ManagedScreen and a ScreenTransition instance as arguments
• ManagedGame#initialize & ManagedGame#create were removed which should eliminate the confusion around the difference between constructors, #create() and #show(); old code should be put in the constructor or #show()
• ScreenTransition#reset was removed in favour of ScreenTransition#show and #hide; old code should be put in #show()
• ShaderTransitions now compile the shader in the constructor; this means that the constructor has to be called on the OpenGL thread
• Use ScreenManager#setAutoDispose(true, true) if you don't want to reuse your screens and transitions and thus they should be disposed automatically upon #hide()
• There were extensive improvements to the javadocs to better document a screen's life-cycle
• Removed the GWT extension

ToDo

• Bring examples up to date and move them into their own Gradle sourceSet, so they can actually be run when the project is imported into an IDE
• Adapt the wiki (https://github.com/crykn/libgdx-screenmanager/wiki/Quickstart, https://github.com/crykn/libgdx-screenmanager/wiki/Screen-Lifecycle, https://github.com/crykn/libgdx-screenmanager/wiki/Lifecycle-Example, https://github.com/crykn/libgdx-screenmanager/wiki/How-to-use-GL-Transitions, https://github.com/crykn/libgdx-screenmanager/wiki/How-to-create-complex-transitions, https://github.com/crykn/libgdx-screenmanager/wiki/Where-to-initialise-screens-and-transitions, https://github.com/crykn/libgdx-screenmanager/wiki/Config-Options) accordingly
• Also update the instructions on getting started to reflect the GWT changes