Move all GA and GTM code to end of body tag

Change description

GTM/GA loading is interfering with the YouTube API. While Google likes you to put a script tag at the top of <head> it is supposed to all work even in body, just means there is a bit more delay in initializing and sending data to Google, and could mean some tracking could get missed if a user bounces off the page before it completes loading. Given the use case is generallly interested users, it's probably fine.

So the code is moved out of head-extra and added to body-extra. Seems to be OK, testing on devstack, but it's a little bit hard to get a good real-world use case so I'd like to try it on Tahoe Staging.

Type of change

[x] Bug fix (fixes an issue)
[ ] New feature (adds functionality)

Checklists

Development

[x] Lint rules pass locally
[ ] Application changes have been tested thoroughly
[ ] Automated tests covering modified code pass

Security

[x] Security impact of change has been considered
[x] Code follows company security practices and guidelines

Code review

[x] Pull request has a descriptive title and context useful to a reviewer. Screenshots or screencasts are attached as necessary
[ ] "Ready for review" label attached and reviewers assigned
[ ] Changes have been reviewed by at least one other contributor
[x] Pull request linked to task tracker where applicable

appsembler / edx-theme-customers