Fix skill level mod not applied to skill granted by items

[mauriliogenovese]

Fixes #591 .

Description of the problem being solved:

Skill level bonus is now applied to skill granted by items

Steps taken to verify a working solution:

import the text build and add a custom modifier +x to level of all spell skills

Link to a build that showcases this PR:

test build

Before screenshot:

After screenshot:

[mauriliogenovese]

this PR may not be necessary as #589 fix the same issue, too