[Tagging] Further refinements to tag drawer

[bradenmacdonald]

1. Please increase the padding around the top and sides of the tagging drawer (it can be increased by 50-100%).
   
2. Please reduce the size of each of the headings in the tagging drawer:
   • The H2 should be kept as <h2> but should look like an H3
     
   • The “Manage tags” heading should match the size of the H4 (18px)
     
   • The Taxonomies headings should should be H3 (not H4) since the next heading above them (the unit name) is H2. However, please change them to look visually like H5.