Minor code cleanup and adjustments

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Refactor filesystem navigation into a new class

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Define string resources and player activity parameter constants

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>