pre fill username in case of github
OS X Keychain:
 * use Security directly, avoid using own native library
 * use "IntelliJ Platform Settings Repository" as service name — more correct and readable
 * fix modification of SSH password (we must use account name (SSH file) instead of host)
 * fix error "An invalid record was encountered." — we must release pointers

 IDEA-131349 Plugin Settings Repository: unable to switch github account