Implement multi-use items.

[scurest]

When using an item, only one "use" should be used up now.

A quick test in RM2K showed

• the number of uses resets when an item is removed
• the number of uses stays the same when an item is added, even if the player already had x99 of the item

Also, for the same reason as #399, using a special item in battle consumes a number of uses equal to the number of targets, currently.

[Ghabry]

Jenkins: ok to test

[fdelapena]

Thanks @scurest! In order to get automatic Jenkins pull requests building for automated tests in multiple platforms, please accept the "Player team" invitation from GitHub to get your user whitelisted in the Jenkins Continuous Integration service. This will prevent the need of the "okay to test" comment for every opened pull request.