Implement sticky header in ItemTable

[campb303]

To allow for a easier sense of place when scrolling through the ItemTable, a sticky header should be implemented. By default, the header should appear flat, being raised with a subtle shadow underneath to indicate that the user is no longer at the top of the table.

A fixed header is supposed in MUI as detailed here. #30 notes how useScrollTrigger can be used for conditional styling based on scrolling.

Example: Sticky header with shadow on scroll:

Image from Design better data tables by Andrew Coyle on Medium

[campb303]

This was put on hold due to issues with parent CSS. The "sticky" header only works when no parents of the element have an overflow setting. This should be revisited after #49

[campb303]

The filters of the ItemTable should be fixed on scroll making them always viewable.

[campb303]

This should be put on hold while a #164 is worked on.

[campb303]

Moved to v2 milestone.

[campb303]

This was fixed in this commit.