Define Siamese network and Prototypical network classes

[tkarab]

Siamese network

• [x] Define class thats inherit the 'keras.Model' class

class init() should include

• [x] feature extractor

• [x] f function

• [x] input shape

• [x] Override the .call() method

• [x] test whether it can be trained

• [x] #73

• [ ] #76

Prototypical Network

• [ ] Class definition
• [ ] init and call
• [ ] N and k should be included in this case