TextSnifferAddon: Move includes out of namespaces

TextSnifferAddon: Fix warnings

TextSnifferAddon: Use MIME DB directly

A DatabaseLocation is passed to the constructor and used to verify that
the sniffed MIME type is installed instead of BMimeType::IsInstalled().
This makes the add-on independent of the default MIME DB.

registrar: Move more classes to libstorage_kit_mime.a

Move MimeSnifferAddon, MimeSnifferAddonManager, and TextSnifferAddon to
libstorage_kit_mime.a, so we can reuse them.

TextSnifferAddon: Move includes out of namespaces

TextSnifferAddon: Fix warnings

TextSnifferAddon: Use MIME DB directly

A DatabaseLocation is passed to the constructor and used to verify that
the sniffed MIME type is installed instead of BMimeType::IsInstalled().
This makes the add-on independent of the default MIME DB.

registrar: Move more classes to libstorage_kit_mime.a

Move MimeSnifferAddon, MimeSnifferAddonManager, and TextSnifferAddon to
libstorage_kit_mime.a, so we can reuse them.