Make API welcome message configurable

This allows flexible, informal messages and, if necessary, terms of
service to be displayed.  For RKorAPClient this is nice because the
welcome message will be displayed on connect.

Change-Id: I9d3c6cef7b1f0205a23fe847909bca0de982bc0f
diff --git a/full/src/main/resources/kustvakt.conf b/full/src/main/resources/kustvakt.conf
index 62546c6..a9086ba 100644
--- a/full/src/main/resources/kustvakt.conf
+++ b/full/src/main/resources/kustvakt.conf
@@ -12,6 +12,7 @@
 ldap.config = file-path-to-ldap-config
 
 # Kustvakt
+api.welcome.message = Welcome to KorAP API!
 current.api.version = v1.0
 # multiple versions separated by space
 # supported.api.version = v1.0