Add map settings to backend. Install leaflet assets to render maps.

db/seeds.rb

@@ -80,6 +80,7 @@ Setting['feature.budgets'] = true
 Setting['feature.signature_sheets'] = true
 Setting['feature.legislation'] = true
 Setting['feature.community'] = true
+Setting['feature.map'] = true
 
 # Spending proposals feature flags
 Setting['feature.spending_proposal_features.voting_allowed'] = nil
@@ -108,3 +109,8 @@ Setting['min_age_to_participate'] = 16
 
 # Proposal improvement url path ('/more-information/proposal-improvement')
 Setting['proposal_improvement_path'] = nil
+
+# City map feature default configuration (Greenwich)
+Setting['map.latitude'] = 51.48
+Setting['map.longitude'] = 0
+Setting['map.zoom'] = 10