core: introducing the scanner interface
core: moving timeout on scanner
core: pv now references scanner instead of director.
core: collectors can send notifications.
core: collectors can send notifications.
sample: new scanner load test can measure time to start pvs and average load
core: first prototype for passive scanner.
Proof of concept to see whether the separation can work.
Not fully working yet.
sample: test scanning on read only
core: avoid npe
core: different handling of calculation exception
core: also collectors that are not associated with datasource recipes should get registered.
core: passive scanner should reschedule notification if new event arrived while notifying previous.
test: making test more robust
Merge branch 'master' into passive_scanner

Conflicts:
	pvmanager-core/src/main/java/org/epics/pvmanager/PVReaderDirector.java
formula: now histogram changes the range
graphene: temporary fix so that the full range of the axis is the range of the cells.
vtype: fixed warning
Next release is 2.8.0
Merge branch 'passive_scanner'

Conflicts:
	pvmanager-graphene/src/main/java/org/epics/pvmanager/graphene/HistogramGraph2DFunction.java
core: adding creation stack trace for unclosed pv