Allow loading config from string

Will be handy for testing
Wrap List<ServerConfig> in SystemConfig, update RunLocal
Add Parser
Remove empty file
Pick random node in FileSender
Add test stub
Add mkdir command
Merge branch 'master' into dev

Conflicts:
	src/main/java/Client.java
	src/main/java/client/FileSender.java
Fix ls cli command argument parsing
squashed: synchronization and additive replication