feat: method / property name aliases closes #31

[Iristyle]

• allows for configuration of custom types, so that the "name" property is displayed in the drop-down, but the "insertion" property determines inserted text

[Iristyle]

Example of how this is used

"instance_properties": [
    {"name": "[ngMock] errors", "insertion": "errors"}
]

Or

"instance_methods": [
    {"name": "[ngMock] mode", "insertion": "mode", "args": [
        {"name": "name", "insertion": "'rethrow'|'log'"}
    ]}
]