Update increasing velocity models

[keurfonluu]

• Changed: improved how initial population is initialized for increasing velocity models.
• Changed: pass option x0 to minimize.
• Changed: temporarily disable option for CMAES and VDCMA.

Reminders:

• Run invoke format to make sure the code follows the style guide,
• Add tests for new features or tests that would have caught the bug that you're fixing,
• Write detailed docstrings for all functions, classes and/or methods,
• If adding new functionality, unit test it and add it to the documentation.