[nix] support storing of string features
[nix] cleanup some metadata saving issues
[beats] add option to provide a custom name, set it as ident of OutData
[savefiles] use repro ident to define the stimulus names
[receptivefield] accelerate y-compensation
[receptivefield] add binwidth to options, interrupt should end repro properly
[receptivefield] use the y_slope correction when moving to best position
[receptivefield] fix inverted z correction