Address remarks after tutor's review

[Gelio]

My tutor gave me many remarks about the thesis contents. Let's incorporate some of them.

The main ones include:

• [x] Move figure captions to the text.
• [x] Try to get figures to appear next to the text that references them.
• [x] Do not refer to the "EMF metamodel". It's the "metamodel for the CAL language built in ECore".
• [x] Make the communication synchronous in the sequence diagrams
• [x] Mention model validation in the thesis results
• [x] Describe M0, M1, M2, M3 levels of metamodelling
• [x] Refer to the UML specification, same with BPMN and MOF
• [x] Explain why we use ApplicationDataPin and not DeclaredDataPin
• [x] Add a list of listings. Show it next to the list of tables