Add support for interact title

[philippjfr]

Fixes #183

[codecov-io]

Codecov Report

Merging #266 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #266      +/-   ##
==========================================
+ Coverage   89.17%   89.19%   +0.02%     
==========================================
  Files          34       34              
  Lines        5523     5534      +11     
==========================================
+ Hits         4925     4936      +11     
  Misses        598      598

Impacted Files	Coverage Δ
panel/tests/test_interact.py	100% <100%> (ø)	⬆️
panel/interact.py	73.68% <100%> (+0.3%)	⬆️

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