Change interface for palettes to be more consistent

[pl0xz0rz]

Previously, the interface for palettes was inconsistent - the "colors" argument took a string that encoded the palette's name, while the "palette" argument took an array that was the palette itsef. With this PR, both interfaces work for both palettes. This PR also fixes a missing import math statement in test_bokehDrawSA.py that got there by some chain of transitive star imports and changes the default palette to kBird256 #278

[miranov25]

Unit test OK:

------------------------------------------------------------------------------------------------ JSON report ------------------------------------------------------------
------------------------------------
report saved to: test6.json
====================================================================================== 37 passed, 7 warnings in 53.54s ======================================================================================

real    0m54.900s
user    12m54.504s
sys     0m45.940s

[miranov25]

Working well also for the real use case: file:///lustre/alice/users/miranov/NOTES/alice-tpc-notes2/JIRA/ATO-614/dEdxWithGasGain.html

Checking the Root palettes I would like to enable also Rainbow - my favorite.

https://root.cern.ch/doc/master/classTColor.html

[miranov25]

I am merging. We can ask Berkin to implement also kRainbow