Feature: Next set of endpoints

[ddxv]

New endpoints

/apps/keywords/{keyword} — returns related apps
/apps/explorer/ — filter by category, installs, store; sort by monthly/total installs
/apps/sdk-explorer/ — filter/sort by company SDK + category/installs
/companies/{domain}/new-apps — apps recently found using the SDK (both buckets: all new + confirmed added)
/companies/{domain}/removed-apps — apps that dropped the SDK between versions