Implemented ApplicationManager

[raul1ro]

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Changes

• [x] Internal code
• [x] Library interface (affecting end-user code)
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Closes Issue: #2713

Description

Implemented ApplicationManager to be able to edit the application assigned to the bot. Discord docs: https://discord.com/developers/docs/resources/application#edit-current-application Implemented only the fields: description, icon and cover_image.

Changes:

• Added interface ApplicationManager and class ApplicationManagerImpl
• Added field Route.Applications.EDIT_BOT_APPLICATION
• Added field JDAImpl.applicationManager and getter JDA::getApplicationManager