[DOCS] Typo on shingle tokenfilter
Removed needless concreteIndices call, already called in doExecute and set to the request object
The mpercolate api rest endpoint should also support http get.
Fixed bug (NPE) in mpercolate api, defaults from percolating existing documents where also applied for the regular percolate api, these defaults were none existing (null).
[DOCS] Fixed percolate docs errors
Randomize exceptions when file is deleted while still open.

This somehow emulates a behavior on windows but we should test the
other code paths as well.
# ContextSuggester

This commit extends the `CompletionSuggester` by context
informations. In example such a context informations can
be a simple string representing a category reducing the
suggestions in order to this category.

Three base implementations of these context informations
have been setup in this commit.

- a Category Context
- a Geo Context
- a Field Context

All the mapping for these context informations are
specified within a context field in the completion
field that should use this kind of information.