PLSTM extension to mark timegate as trainable True/False

[ntlex]

Hi there,

I have added a small extension to your implementation, to enable the timegate to have a trainable True/False as the authors do in the paper. Switching to trainable=False gives you the opportunity to work with custom weights for the shift, period and ratio and have fixed oscillations. This is particularly useful for those who want to use the PLSTM to sync multiple channels of different modalities (e.g. vision, audio, nlp etc).