Fix character trimming in xml parser

Fix character trimming in xml parser

[Problem] ASCII tag content is being trimmed and it shouldn't be.
[Solution] Don't trim tag content in Characters() callback. If trimming is
necessary it can be done in End() callback. Exception will be thrown only if
non-whitespace characters are found within tags that shouldn't have any
character content (InitialValueHandler, PermissionHandler).

[Verification] Run ckm-tests --group=T60_INITIAL_VALUES

Change-Id: I39a928bf15be29ade96986d619c9023fb4cd3234