changing append to extend for adding base class attribute code. Also adding real and imag properties to the gauss_param object to reflect that it is a complex number

Added abstract class for mirror and beamSplitter classes, providing all of the shared functionality.

mirror params.

adding in gauss_param object. Although it doesn't inherit from a complex type it can be used as one in equations as it overrides the various options

want to use things such as '1n' in pykat, it just needs
to be used during the init constructor which is used when
reading finesse code.

objects that have properties dynamically added to themselves need to declare themselves as new classes, with a base class of the original. Otherwise when we add properties we add them to all instances.

completly changing how node connections are stored: node_network (kat.nodes) now stores all the information regarding which node is connected to which component and vice-versa. If any of these connections change it is handled in node_network. All the compoents and nodes no longer store the connection information locally, they must reference directly from node_network otherwise weird clashes will occur. Not fully tested yet.

demodulations.