Minor code improvements on LIonWeb

[psuzzi]

I took a look at the com.strumenta.kolasu.lionweb, and found a few improvements I suggest to implement:

• Use of when statements instead of nested if-else ones, e.g. in JSONComparison
• get rid of the .asJsonObject in favor of is smart-casting, e.g. in JSONComparison
• Add the JsonPrimitive case in JSONComparison
• Apply @Synchronized instead of explicit synchronized blocks, e.g. in BiMap
• execute containment checks with the in operator instead of containsKeys(), e.g. in BiMap
• improve thread safety with mutex.withLock, e.g. in PerformanceLogger
• add a try - finally block where operations are executed, e.g. in PerformanceLogger#log

A PR will follow