Don't differentiate between vertex and index count in Mesh.

Only one value from these two was used in the end, wasting precious
bytes. Also these two values were used to differentiate between indexed
and non-indexed mesh (instead of relying on actual index buffer being
bound), which was very confusing. This approach looks more clean. The
MeshView class is not yet updated, as the change would expose some
features that aren't possible in current implementation (base vertex
specification).

Merged Mesh::setVertexCount() and Mesh::setIndexCount() into one
Mesh::setCount(), the two original functions are now guarded aliases to
the new one, are marked as deprecated and will be removed in future
release, similarly for the getters.

In particular, if the mesh is indexed, setVertexCount() does nothing and
vertexCount() returns 0. The setIndexCount() and indexCount() do and
return the same regardless of whether the mesh is indexed or not.
Ability to specify base vertex in Mesh.

The well-known issue is that gl*DrawElements*BaseVertex() is not
supported in OpenGL ES. It is possible to work around it by
reconfiguring whole VAO, but that seems to be a bit overkill. Currently
the draw() function just asserts that base vertex is not specified for
indexed meshes.
Updated MeshView to reflect changes in Mesh.

Added base vertex specification, not differentiating between vertex and
index count. The old setVertexRange(), setIndexRange(4) and
setIndexRange(2) are now aliases to new setCount(), setBaseVertex(),
setIndexRange(3) and setIndexRangge(1) functions, are marked as
deprecated and will be removed in future release.
Added test for mesh base vertex.
MeshTools: deprecate mesh/buffer-modifying vertex/index tools.

The point of this change is to allow greater flexibility and reduce
confusion.

When instanced meshes are implemented, MeshTools::interleave() can be
used for creating interleaved buffers with per-instance data and then
the call to Mesh::setCount() will be harmful and/or confusing, becuase
the user would in fact want to call Mesh::setInstanceCount() instead.
Similarly, MeshTools::compressIndices() can be used to create index
buffer for more than one mesh.

GL 4.4 has ARB_buffer_storage, which (in relatively distant future) will
mean that the current way of Buffer::setData() will be deprecated in
favor of Buffer::setStorage(), similarly as Texture::setStorage()
replaced Texture::setImage(). Thus any function which calls
Buffer::setData() internally is not future-proof.

The old MeshTools::compressIndices() and MeshTools::interleave()
overloads are marked as deprecated and will be removed in future
release.
Added some TODOs related to buffer storage.
Max texture LOD bias _is_ available in OpenGL ES 3.