Create definitions for standard DHCP options

Both the server and the UI need to understand formats of the DHCP options. We need some uniform way to define option formats. The main goal is to generate an option template in the host reservation form that already has appropriate fields added, so the user doesn't need to remember the option definitions. The server needs to understand the options returned by Kea, validate them and convert into the format acceptable by the UI client. For example, it must understand whether the option field is a uint8, uint16 or uint32. This can't be guessed from the returned option data.