Fix WebGlContextLost handling.

Maybe "clearBeforeRender" this is not the best naming (since it will clear anyway..), but this aligns canvas and webgl:

Basically it allows the user to do clearColor whenever they want, instead of this being done for them. This is useful in the following circumstance:

1) The game/program loads a background image, but not right away.
2) Before the background image is loaded, we want to fill the canvas with a certain color (for example, white).
3) In canvas mode, this is done by setting ``clearBeforeRender`` to false and then adding a single ``fillRect`` command.
4) In webGL mode, the equivalent is running ``gl.clearColor`` and then ``gl.clear``.
5) We can of course set the background color in webGL mode and this probably won't be expensive (although I don't know), but in canvas it *is* expensive to clear/fill on every frame.
6) Thus, the user would have to detect webGL mode or canvas mode themselves, and either set the background color or not.
7) To eliminate this coding complexity for the user, this small bit of extra code aligns ``clearBeforeRender`` (or, as much as possible) to the canvas implementation.

oops!

fixe ios8 rendering issue

resolution will now match the renderer resolution

Interactive Manager
BaseTexture
Text
WebGLRenderer

Sprites / Graphics / Text

In WebGlRenderer.js, this.contextLost was being used both as a function
created by bind() and as a boolean variable. Not only is this
incorrect, it also would cause problems in Firefox when calling
removeEventListener, as it would expect contextLost to be a function,
but instead it would get a boolean and would raise an error. Chrome did
not raise an error when calling removeEventListener with a boolean
value as the second argument instead of a function.

This patch separates the two uses of this.contextLost, which is how it
should be.

Fixed webGL Blend mode issue
Fixed render texture alpha issue
Fixed Canvas tinting issue

Fix WebGLStencilManager.destroy method to destroy the stencilStack