blur: use common shader sources
blur: use common shader sources

Port blur filter to use the common convolution shaders in
gstgleffectssources.c. This reduces code duplication and, incidentally,
the shaders in the common file were already updated to not use array
constructor and to not depend on #version 120.
First step towards bug #615696 fixing.

ystreet/gst-plugins-gl,ystreet/gst-plugins-gl,mapmapteam/gst-plugins-gl,mapmapteam/gst-plugins-gl,ystreet/gst-plugins-gl,mapmapteam/gst-plugins-gl