allow getMetas without synchronized

diff --cc src/be/nikiroo/fanfix/library/BasicLibrary.java
Simple merge

diff --cc src/be/nikiroo/fanfix/library/CacheLibrary.java
Simple merge

diff --cc src/be/nikiroo/fanfix/library/LocalLibrary.java
Simple merge

diff --cc src/be/nikiroo/fanfix/library/RemoteLibrary.java
Simple merge