EMI: Fix position of attached actor

When attaching an actor to another one, set its local position
so that its final position (position of the parent actor + the
local position) remains the same as the final position before
it was attached.
BUILD: Conditionally include shaders
MYST3: Introduce shader-based renderer
MYST3: Move OpenGLTexture into separate file
GRAPHICS: Update system_headers.h for regular OpenGL
MYST3: Separate renderers into separate classes
JANITORIAL: Remove g_ prefix from instance variables
MYST3: Support Text rendering [OpenGLS]
MYST3: Dialog movies are also localized
MYST3: Don't needlessly center the mouse when changing nodes
MYST3: Reset viewport in menus
Merge pull request #825 from PoulpiFr/running-manny

ANDROID: Quick changement to the touchcontrols to let Manny run + Overlay buttons on screen
EMI: Update shader for actors and sprites [OpenGLS]
Merge pull request #834 from Botje/myst-es2

MYST3: ES2 backend
MYST3: Explain the texture size workaround used in the ES2 renderer
MYST3: Clamp cube textures in the ES2 renderer

This effectively implements GL_CLAMP_TO_EDGE in the shader
for 3D objects, solving the issue described in 61968c6.
Merge pull request #822 from chkr-private/item-drawing-fixes

EMI: Rotation of (attached) actors
update credits
GRIM: Fix typos in include guards
Merge pull request #836 from salty-horse/include_guards

GRIM: Fix typos in include guards