SeedingData: use the GraphPath storage code to compute seeds

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
SeedingData: refactor code so that m_content is abstracted

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
SeedingData: use 2-bit encoding for paths

Resolves-bug: https://github.com/sebhtml/ray/issues/144
Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
SeedingData: plugin options are parsed by plugins

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
use constants for symbols

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>