Improve resource scanning flow (#68)

* List supported resources for scanners

* Don't warn on scanner discovery commands

* Use scanner-to-resource map

* Save changes

* Scan result tabs

* Own table render for Checkov

* Scannable manifest flag for scanners

pkg/dashboard/subproc/scan.go

@@ -5,6 +5,8 @@ type Scanner interface {
 	Test() bool                                                             // test if the scanner is available
 	ScanManifests(mnf string) (*ScanResults, error)                         // run the scanner on manifests
 	ScanResource(ns string, kind string, name string) (*ScanResults, error) // run the scanner on k8s resource
+	SupportedResourceKinds() []string
+	ManifestIsScannable() bool
 }
 
 type ScanResults struct {