Improve JS Initialisation that we do on each page

What does this MR do?

Improves setup of main.js and header.js so that during initialisation we defer load to a later point. This is a first incremental step but definitely more to come. This reduces time to first paint and time of execution for domContentLoaded

Moved Initialisations in 'main.js' to function (deferredInitialisation) which is executed through requestIdleCallback. This executes normally ms after the first rendering is done.

• Init BreadCrumbs
• Init Importer Status
• Init Todo Toggle
• Init Logo Animation
• Init Search Autocomplete
• Init Performance Bar if there is one
• Focus Behaviour
• Global Ajax Handling
• Awards Handler

header.js

• requestIdleCallback for initialisation of the User Status Modals

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer