Improve duplicated ignored files

[el-teedee]

Ignored files can be declared given their filename only (not the path, neither relative, or absolute).
If multiple files have same name in the plugin, they will all be ommited. (ex: thumbnail.jpg for differents resources).

Improvement: make the declaration "unique"

Exemple of current declaration:

excluded.files = thumbnail.jpg

Proposed declaration:

excluded.files = **/images/**/thumbnail.jpg

Relates to: #4