update kirby to v5 and add refresh cache panel view button

public/site/plugins/refresh-cache-button/SECURITY.md

@@ -0,0 +1,18 @@
+# Security Policy
+
+## Supported Versions
+
+*Use this section to tell people about which versions of your project are currently being supported with security updates.*
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 5.1.x   | :white_check_mark: |
+| 5.0.x   | :x:                |
+| 4.0.x   | :white_check_mark: |
+| < 4.0   | :x:                |
+
+## Reporting a Vulnerability
+
+*Use this section to tell people how to report a vulnerability.*
+
+*Tell them where to go, how often they can expect to get an update on a reported vulnerability, what to expect if the vulnerability is accepted or declined, etc.*