Slot Waveguides

These are slot and double slot waveguides:

`SlotWaveguideTemplate`	This waveguide is a strip-like waveguide with a slot in the middle.
`DoubleSlotWaveguideTemplate`	This waveguide is a strip-like waveguide with two slots in the middle

Transitions

The following transitions to a rib waveguide have been defined:

`SlotWaveguideTransitionFromPortLinear`	A linear transition between two SlotWaveguideTemplates, starting from a port.
`SlottedWireWaveguideTransitionLinear`	Transition from/to a slotted waveguide to/from a wire waveguide.
`SlottedWireWaveguideTransitionFromPortLinear`	Linear transition from/to a slotted waveguide to/from a wire waveguide.