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/lite/src/main/resources/kustvakt-lite.conf b/lite/src/main/resources/kustvakt-lite.conf
index e78f993..9dc83b5 100644
--- a/lite/src/main/resources/kustvakt-lite.conf
+++ b/lite/src/main/resources/kustvakt-lite.conf
@@ -13,6 +13,7 @@
 
 # Kustvakt settings
 
+api.welcome.message = Welcome to KorAP API!
 current.api.version = v1.0
 # multiple versions separated by space
 supported.api.version = v1.0