Update references; add pEp 4 Thunderbird.

shared/references/implementation-status.mkd

@@ -19,3 +19,7 @@
     target: https://enigmail.net/index.php/en/download/source-code
     title: Source code for Enigmail/pEp
     date: 2020-07
+  SRC.pepforthunderbird:
+    target: https://pep-security.lu/dev/repos/pEp_for_Thunderbird/
+    title: Source code for pEp for Thunderbird
+    date: 2020-07

shared/text-blocks/implementation-status.mkd

@@ -28,12 +28,13 @@ The following software implementing the pEp protocols (to varying
 degrees) already exists:
 
 * pEp for Outlook as add-on for Microsoft Outlook, release {{SRC.pepforoutlook}}
+* pEp for iOS (implemented in a new MUA), release {{SRC.pepforios}}
 * pEp for Android (based on a fork of the K9 MUA), release {{SRC.pepforandroid}}
-* Enigmail/pEp as add-on for Mozilla Thunderbird, release {{SRC.enigmailpep}}
-* pEp for iOS (implemented in a new MUA), beta {{SRC.pepforios}}
+* pEp for Thunderbird as a new add-on for Thunderbird, beta {{SRC.pepforthunderbird}}
+* Enigmail/pEp as add-on for Mozilla Thunderbird, release (will be discontinued early 2021) {{SRC.enigmailpep}}
 
-pEp for Android, iOS and Outlook are provided by pEp Security, a commercial
-entity specializing in end-user software implementing pEp while Enigmail/pEp
-is pursued as community project, supported by the pEp Foundation.
+pEp for Android, iOS, Outlook and Thunderbird are provided by pEp Security, 
+a commercial entity specializing in end-user software implementing pEp while 
+Enigmail/pEp is pursued as community project, supported by the pEp Foundation.
 
-All software is available as Free Software and published also in source form.
+All software is available as Free Software and published also in source form.