add getters for VirtualFileSystem.setContainer()

Maybe people want to know...  include getContainerPath() since that is how
the data is actually stored.
alternate form of mount() that includes path to container file

In some situations, it'll make more sense to do a single call to mount()
with all relevant information rather than setContainer() then mount().
update libsqlfs submodule to get new raw key API

libsqlfs now as separate methods for opening using raw key data, which
SQLCipher will use directly, or using a password, which SQLCipher will use
to derive a raw key with.

refs #3174 https://dev.guardianproject.info/issues/3174
REWORD convert key type to char[] to allow zeroing

expose new raw key API in Java, to work better with CacheWord

CacheWord generates the raw key based on a dynamic number of iterations of
the KDF, so that it doesn't take ridiculously long on old devices, but on
new devices has a reasonable number of KDF iterations.  The exposes that
API into IOCipher's Java interface for easy integration with CacheWord.

refs #3174 https://dev.guardianproject.info/issues/3174