Renamed Param expand options

[philippjfr]

• Closes Add subpanel expansion options #69

[codecov-io]

Codecov Report

Merging #127 into master will not change coverage.
The diff coverage is 95.65%.

@@           Coverage Diff           @@
##           master     #127   +/-   ##
=======================================
  Coverage   89.76%   89.76%           
=======================================
  Files          27       27           
  Lines        4025     4025           
=======================================
  Hits         3613     3613           
  Misses        412      412

Impacted Files	Coverage Δ
panel/tests/test_param.py	99.61% <100%> (ø)	⬆️
panel/param.py	90.27% <93.75%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bb7a42e...94df6c0. Read the comment docs.

[jbednar]

Looks great, thanks!