add copybutton from cpython sources

allows toggling the input markers in source examples to allow
copy & pasting them.
remove minified jquery

the sphinx installation must be enough, we don't need two.
Remove minified bootstrap --- the bootstrap JS components are not used
Merge branch 'pr-4'

MAINT: Remove minified bootstrap and jquery javascript, add copybutton

Bootstrap JS components are not required, and Sphinx already ships with
jquery.