refactor: add `dissolveNamespace` as configuration option and update docs

[ThorstenSuckow]

The semantics regarding root and subscriptions have changed.

This must be reflected in documentation, configuration and the API.

• subscriptions are the folders a client is interest in when querying mail folders, similiar to IMAP subscriptions.
• dissolveNamespaces are namespaces that are dissolved when reading folder structures and returning to the client.

see php-lib-conjoon#28

[ThorstenSuckow]

add options to resource query in e3f6b90

[ThorstenSuckow]

The Resource\Query\MailFolderListQuery no provides an interface for retrieving MailFolderListOptions, which in turn encapsulates the dissolveNamespaces option.