VBO_CONTAINER: Changed new[]/delete[] pairs to realloc(), possibly reducing memory fragmentation and the container shrinking time.

Faster circles & semicircles drawing for the shaderless OpenGL backend. Removed unnecessary variables and computations.

- VBO_CONTAINER::allocate() was returning wrong value in case of error
- framelimiter had wrong formula for computing destined period between frames
- removed _padding field from VBO_VERTEX, as it was not speeding up, but wasting memory

Now it does not use all the CPU power while panning even on simple boards.

Changed order of used headers, so there is no need to include again 'wx/wx.h' needed by layers_id_color_and_visibility.h

Moved fields containing information about currently used color, shader and transformation for vertices from VBO_ITEM to VBO_CONTAINER (OPENGL_GAL).

Added VBO_CONTAINER as a faster storage for vertices (OPENGL_GAL), tuned for exchanging data with GPU.

Removed a few unnecessary variables and fields from OPENGL_GAL.
Added function GAL::ClearCache() for freeing memory used by cached items.
Fixed a few memory leaks (tesselator, PAINTER's settings & VIEW_ITEM's groups).
Changed a few functions into inlines.

Removed indices storing from VBO_ITEM as they are always consecutive numbers. Removed storing pointers to VBO_ITEMs that have to be drawn - instead they are memcpied to mapped GPU memory.
Some functions of VBO_ITEM became inline.

which was creating silly strings like 

  PcbTextThickness="    0.300000"

in kicad.pro files.

Switching to OpenGL using shaders backend on the fly (changed keyboard shortcuts: different backends are available using Alt+F9..F12).

Shader's parameters are stored in VBO_ITEM. Changed VBO_ITEM data structure. Added UseShader() function for selecting shader for a given VBO_ITEM.
Added one main vertex & fragment shader program to be used for with all kinds of items (type of shader is selected using attributes that are stored in VBO). Currently available shaders are: at-least-1px-width line, filled circle and stroked circle.
Removed unnecessary param (aDepthOffset) from a few functions (OPENGL_GAL::drawSemiCircle(), OPENGL_GAL::drawLineCap()). Removed function OPENGL_GAL::DrawRoundedSegment(). Changed some asserts to debug info or error log.