feat: Updates and fixes for vcf-report

[fxwiegand]

This PR includes multiple small fixes and additions to rbt vcf-report.

• Allele frequency plot in level 2 is now plotted as a heatmap (width adjusted to # of samples)
• Plot titles and axis are now positioned at the top to reduce scrolling
• Searching icon moved to the navbar to save space
• Fix for the searching functionality caused by wrong import order of js files
• Update to latest Bootstrap 4 version
• Typos
• Update CLI help for VEP options (see #205)