Fixed a slow id generator rebuild high id issue

where the high id would be set too high.
Also removes a test that, using complicated breakpoint testing, basically
tested that IdGeneratorImpl#setHighId throws exception when given -1 as
high Id. Replaced with a unit test.
Fix formatting of the description of the mapped_memory_total_size configuration
Fixes an issue where id generator picked up freeId calls during recovery

where it shouldn't have done so. It's due to a recent change removing the
recovery flag for the stores. Now setStoreNotOk() sets idGenerator null so
that even if the id generator was opened cleanly, but later we found out
that the store needed recovery we would clear it so that the id generator
wouldn't pick up freeId calls during recovery.
Remove metadata/id from the representation

Pending discussion on its format
ExpandPipe should use relation type indices when possible

This change lets ExpandPipe use relationships ids instead of names whenever all ids in question are resolved.
Return null instead of throwing SchemaRuleNotFoundException when index not found
VarLengthExpandPipe uses token ids whenever possible.

When all relationships tokens are resolved VarLengthExpandPipe
uses these instead of using the name.
Merge pull request #3151 from cleishm/metadata_no_id

[2.1] Remove metadata/id from the representation
Merge pull request #3146 from tinwelint/2.2-freeid-during-recovery-fix

[2.2] Fixes an issue where id generator picked up freeId calls during recovery
Merge branch '2.1-maint'
Merge pull request #3142 from tinwelint/2.2-too-high-id-after-slow-rebuild

[2.2] Fixed a slow id generator rebuild high id issue
Merge pull request #3147 from chrisvest/2.2-pagecache-docs

[2.2] Fix formatting of the description of the mapped_memory_total_size configuration
Merge pull request #3155 from lutovich/2.1-no-exceptions-for-flow-control

[2.1] Return null instead of throwing SchemaRuleNotFoundException when index not found
Merge branch '2.1-maint'

Conflicts:
	community/kernel/src/main/java/org/neo4j/kernel/impl/api/StateHandlingStatementOperations.java
Merge pull request #3153 from pontusmelke/expand-pipe-using-ids

[2.2] ExpandPipe and VarLengthExpandPipe should use relation type token id when possible
Refactorings and improvements on batch importer staging

The staging framework for the ParallelBatchImporter has been
changed to reduce time spent in the framework itself as well
as reporing much more accurate statistics.

- Simplified Stage to only have #add(Step), instead of input/add
- Simplified and streamlined waiting of conditions in individual steps
  where conditions are first busy waited a little while, to then
  back off to a sleep strategy.
- Improved accuracy of statistics of upstream/downstream idling,
  possible since better placed for measuring was found.
- DetailedExecutionMonitor will find and print which step is the
  current most likely step to be the bottle neck in the stage.
- Correctly and efficiently follows the contract of a step, where
  batches must be sent downstream in the order they arrived, which
  implies total ordering as a whole between steps. Previously there
  was too strict checks such that some parallelization was hindered.