igxGrid - refactor header and filter cell components

[SAndreeva]

Closes #2972, Closes #2926, Closes #2923, Closes #2917, Closes #2783, Closes #3027, Closes #2938.

This PR introduces the following changes that are with high regression potential:

• a new component (header group) to accommodate the header and filtering cell components;
• all column moving and column resizing related DOM structures are moved to the new header group component;
• MCH are hierarchical structure, comprising of these header group components, only the deepest groups should have a header and a filter cell;
• the old header component is cleaned up, it takes care only for sorting;
• column resizing base logic is moved to a separate service;

[SAndreeva]

Close this PR and will create a new one with all changes from 6.2.x