Improve items and collections

[gadomski]

Related Issue(s):

• Closes Take up new 3DEP layout #10
• Closes Possible discrepancy between STAC metadata and COG #9
• Closes License is incorrect #6
• Closes Add package description #3

Description:
Many fixups to items and collections:

• Reads the proj information from the raster itself
• Adds the raster and scientific extensions
• Updates paths to take up the new 3dep data layout

PR checklist:

• Code is formatted (run scripts/format).
• Code lints properly (run scripts/lint).
• Tests pass (run scripts/test).
• Documentation has been updated to reflect changes, if applicable.
• Changes are added to the CHANGELOG.