Center aligned meshes

[ManevilleF]

Closes #136

What does it solve

• Mesh generation was broken if used with an HexLayout with a non zero origin, as the origin offset would be applied twice ( hexagonal_plane + the mesh builders)
• In addition to this, if used with bevy the offset would be also applied by hexagon entities transforms

Solution

• Added a center_aligned builder method to all mesh builders. this negates the HexLayout offset
• Fixed PlaneMeshBuilder::build method which was applying the offset twice

[Godnoken]

It works great with the field_of_movement example and for my own usage. Thank you! 🥇