Add 2 new admin actions (#191)

* Synchronize all gists previews
* Reset Git server hooks for all repositories

internal/web/server.go

@@ -235,6 +235,8 @@ func NewServer(isDev bool) *Server {
 			g2.POST("/sync-fs", adminSyncReposFromFS)
 			g2.POST("/sync-db", adminSyncReposFromDB)
 			g2.POST("/gc-repos", adminGcRepos)
+			g2.POST("/sync-previews", adminSyncGistPreviews)
+			g2.POST("/reset-hooks", adminResetHooks)
 			g2.GET("/configuration", adminConfig)
 			g2.PUT("/set-config", adminSetConfig)
 		}