iti-71: renaming/correction

[ziegm]

@oliveregger please review the changes for issue #51

http://build.fhir.org/ig/ehealthsuisse/ch-epr-mhealth/branches/issue51_iti-71/sequencediagrams.html [ITI-71]:

• rename 'authorization token' to 'access token' according to IHE spec.
• remove 'Exchange code for access token' transactions, because they are included in [ITI-71]