UF fix and various code cleanup

[Ovascos]

This PR provides various code clean-ups and performance optimizations:

• Fixes MCSAT UF Plugin performance bugs #662
• Clean-up code, improve readability by adding const and joining declaration and definitions of variables.
• Adds statistics to count backjump-learn and backjump-decide calculus rule application
• Performance: don't register true_term with mcsat (when a term is solved by the preprocessor)
• Remove dirty trail replacement from mcsat_analyze_final.
• Update header file structure to avoid including big headers for one typedef.
• Adds static to various functions to allow internal linkage

[coveralls]

coverage: 71.198% (-0.01%) from 71.209% — Ovascos:pr into SRI-CSL:master