Added missing English translations.

src/main/resources/assets/org/orekit/localization/OrekitMessages_en.utf8

@@ -110,7 +110,7 @@ UNEXPECTED_END_OF_FILE_AFTER_LINE = unexpected end of file {0} (after line {1})
 UNABLE_TO_PARSE_LINE_IN_FILE = unable to parse line {0} of file {1}:\n{2}
 
 # unable to parse element {0} at line {1}, file {2}
-UNABLE_TO_PARSE_ELEMENT_IN_FILE = <MISSING TRANSLATION>
+UNABLE_TO_PARSE_ELEMENT_IN_FILE = unable to parse element {0} at line {1}, file {2}
 
 # unable to find file {0}
 UNABLE_TO_FIND_FILE = unable to find file {0}
@@ -476,7 +476,7 @@ CCSDS_AEM_INCONSISTENT_TIME_SYSTEMS = inconsistent time systems in the attitude
 CCSDS_AEM_ATTITUDE_TYPE_NOT_IMPLEMENTED = attitude type {0} in CCSDS AEM files is not implemented in Orekit
 
 # invalid rotation sequence {0} at line {1} of file {2}
-CCSDS_INVALID_ROTATION_SEQUENCE = <MISSING TRANSLATION>
+CCSDS_INVALID_ROTATION_SEQUENCE = invalid rotation sequence {0} at line {1} of file {2}
 
 # element set type {0} ({1}) is not supported yet
 CCSDS_UNSUPPORTED_ELEMENT_SET_TYPE = element set type {0} ({1}) is not supported yet