Loosen dependency on log4php by creating Zarafa_Logger shim class

Create separate logging class, which will try to load log4php but silently
fail if that component is not installed; this loosens the dependency on
log4php.
Don't redefine FALSE() if already defined

Necessary when you want to include Sabre-Zarafa in another project that already
defines FALSE(). The author encountered this.
ORG and N: only include in vCard if they contain data

Previously, cards without ORG data were still getting an empty ORG property.