added relationselector and severityvaluesgroup component

[saberlynx]

• added a component "RelationSelector" to select between '=', '<' and '>'. All it does is select relation.
• added a component "SeverityValuesGroup" replacing CvssBaseGroup (it is now more general) that has "RelationSelector" as child, enabling user to do eg. "cvss_base>3"

Checklist:

• Tests
• CHANGELOG Entry

[codecov]

Codecov Report

Merging #1477 into master will increase coverage by 0.03%.
The diff coverage is 95%.

@@            Coverage Diff             @@
##           master    #1477      +/-   ##
==========================================
+ Coverage   36.89%   36.93%   +0.03%     
==========================================
  Files         994      995       +1     
  Lines       22256    22271      +15     
  Branches     6140     6139       -1     
==========================================
+ Hits         8211     8225      +14     
- Misses      12729    12730       +1     
  Partials     1316     1316

Impacted Files	Coverage Δ
gsa/src/web/pages/results/filterdialog.js	50% <ø> (ø)	⬆️
...src/web/components/powerfilter/relationselector.js	100% <100%> (ø)
.../web/components/powerfilter/severityvaluesgroup.js	94.11% <94.11%> (ø)

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[bjoernricks]

Looks good to me.