Optimize PP3 and BP4 VCEPs

[gromdimon]

Is your feature request related to a problem? Please describe.
We have suboptimal implementation of PP3 and BP4 VCEPs.

Describe the solution you'd like
Optimize the implementation:

• Combine methods such as _is_splice_variant _is_inframe_indel, _is_missense_variant, _is_synonymous_variant, _is_intron_variant, _is_utr_variant. They all share same logic, so they can be combined in 1 supermethod with additional parameter(s).
• Improve _affect_spliceAI method by providing one threshold for all spliceAI scores. This threshold is the "delta" score of spliceAI. Change it also in AutoBP7._spliceai_impact and AutoPS1PM5._affect_splicing.
• Change the VCEPs as needed.
• Update unit tests

Describe alternatives you've considered
N/A

Additional context
N/A