add a modern jQuery API and deprecate the old one

fixed in b29

to load jQuery 3 in your stack please use the new API and specify "jquery3" in the libraries dictionary in your stack plist. the "jquery" library (without a version number) is now deprecated.

currently available jQuery versions:

jQuery 3:  ("jquery3")
default:                 jQuery v3.7.1
if maxVersion <= 3.6:    jQuery v3.6.4
if maxVersion <= 3.5:    jQuery v3.5.1
if maxVersion <= 3.4:    jQuery v3.4.1
if maxVersion <= 3.3:    jQuery v3.3.1
if maxVersion <= 3.2:    jQuery v3.2.1
if maxVersion <= 3.1:    jQuery v3.1.1
if maxVersion <= 3.0:    jQuery v3.0.0

jQuery 2 ("jquery2")
default:                 jQuery v3.7.1 + migration
compat mode:             jQuery v2.2.4

older API's and versions are deprecated but still supported for S6 -- and will be removed for S7
using "jquery" library setting, no matter the version requested, results in the Stacks 5 plug-in behavior: jQuery 2.2.4