[NEXUS-5406] Replace static combo box stores with dynamic ones (specified at form field level)

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge remote-tracking branch 'origin/master' into NEXUS-5406-dynamic-source-for-capab-combos
Merge pull request #134 from sonatype/NEXUS-5406-dynamic-source-for-capab-combos

REVIEW: [NEXUS-5406] Dynamic source for capabilities combos