IMPLEMENTATION: Replaced hand-coded UI by a widget manager

This automatically create and manage widgets based on parameters.
Still WIP.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
SYNTH: Parameter count getter now returns an unsigned

For the correctness of correctness.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
SYNTH: Minor comment update

Based on actual usage (in implementation), explained the best way
to iterate over parameters and why it works.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>