4.4.0: Better Flow-Id handling, configurable lock timeouts

This version is for Spring-Boot 1.

Feature: (#116) Better flow id handling for Snapshots
The current versions of tracer-spring-boot-starter do not setup tracing instrumentation for spring boots management endpoints (at least if they are mapped to a different port). Due to this, snapshots triggered via the management endpoints had no flow ids and a warning was logged for each event before sending.

We now create a new trace iff there is none yet in those cases, so that snapshot events will always have a flow id.

Feature: (#120) Configurable lock timeout

When sending events out, we are first locking them for some time so no other process running the same library is trying to send out the same events. With this change, the time for which those events are locked is configurable, which is helpful for applications with low latency and high volume requirements.
Look for lock-duration and lock-duration-buffer in the README if you want to use this feature.

No migration is needed, the default settings behave as before (but might change in the future).

Minor improvement: Some dependencies received some updates