Multiselect varY / varYNorm template

[pl0xz0rz]

This PR adds multiselect varY / varYNorm for the getDefaultVars template

Because "varY-varYNorm" alias is not defined when one of these is a multiselect, it's done by creating multiple histograms and then creating the join, in the template

It also fixes a bug with the Y axis label introduced in #326, a bug making getDefaultVarsRatio also introduced in #326 not work because of a typo and an old bug with scalar histogram weights (possibly never worked properly)

Multiselect varZ / varZNorm not supported for template yet

Example use cases in test_bokehClientHistogram.py

[miranov25]

Tests formaly OK

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
--------------------------------------------------------------------------------------------------------------------------------- JSON report ----------------------------------------------------------------------------------------------------------------------------------
report saved to: test6.json
================================================================================================================== 39 passed, 7 warnings in 101.93s (0:01:41) ==================================================================================================================

real    1m43.761s
user    31m7.128s
sys 3m2.684s

[miranov25]

Unit test looks fine. Merging