Add support for more license_expression fields

[tdruez]

In particular declared_license_expression and other_license_expression following their addition in DejaCode.

[DennisClark]

thanks for logging this issue @tdruez we definitely want support for the two new license fields in aboutcode-toolkit.

[chinyeungli]

Questions:

1. Do the declared_license_expression and other_license_expression also use the Scancode license key/expression, or can they be in other formats, such as a list or a string like 'MIT' (which is invalid, as it should be mit)?
2. When I do the --fetch_license, should these licenses also be fetched and created?

[mjherzog]

These should be standard license expressions with either ScanCode or SPDX license ids (one or the other per expression - no mix & match). We will, of course, have other license names and "expressions" in Scan data, but not in ABCTK.

[chinyeungli]

Another question, for the generated ABOUT file, should the new licenses also "group" into the "licenses"?
Current format

about_resource: test.c
name: test.c
license_expression: mit
declared_license_expression: isc
other_license_expression: mit-0
copyright: robot
licenses:
  - key: mit
    name: MIT License
    file: mit.LICENSE
    url: https://scancode-licensedb.aboutcode.org/mit.LICENSE
    spdx_license_key: MIT

Should it be something like:

about_resource: test.c
name: test.c
license_expression: mit
declared_license_expression: isc
other_license_expression: mit-0
copyright: robot
licenses:
  - key: mit
    name: MIT License
    file: mit.LICENSE
    url: https://scancode-licensedb.aboutcode.org/mit.LICENSE
    spdx_license_key: MIT
  - key: isc
    name: ISC License
    file: isc.LICENSE
    url: https://scancode-licensedb.aboutcode.org/isc.LICENSE
    spdx_license_key: ISC
  - key: mit-0
    name: MIT-0-Clause
    file: mit-0.LICENSE
    url: https://scancode-licensedb.aboutcode.org/mit-0.LICENSE
    spdx_license_key: MIT-0

[chinyeungli]

This is fixed