Fixed blending function for OpenGL compositing. Corrected documentation, removed unnecessary functions.

Code refactorization. VBO_CONTAINER is split to [NON]CACHED_MANAGER, GPU_MANAGER and VERTEX_MANAGER.

Added separate layers for pad netnames (now these are divided into multilayer/top/bottom pads).
More appropriate layers are selecting a copper layer in the high contrast mode (now it shows the copper layer itself, vias & multilayer pads and netnames).

1 pixel wide outlines for the Cairo and the OpenGL with shaders backends, but it breaks displaying outline in the shaderless OpenGL backend.

Refactored code responsible for high contrast mode. Now it allows to have more than one layer on the top.
Selecting layer using the dropdown list on the toolbar influences the layer displayed in high contrast mode.

Scripting engine build fix.

Removed most of deprecated OpenGL calls. Items used to be drawn in immediate mode now are drawn using vertex arrays.

Added implementation of level of details per layer and item type pairs basis (items on every layer have a possibility to define the minimum VIEW scale to be shown).

Added the 'cached' parameter for VIEW_LAYER. The parameter decides if items drawn on the layer should be cached or drawn in immediate mode.
Removed m_useGroups from VIEW, as now groups are enabled per layer.

Fixed drawing of lines' caps.

Fixed drawing stroked semicircles using OpenGL backend.