be more explicit about updatemode, add javadoc

add what was the default/null updatemode (create) and add
documentation about intentions of behavior. add test to verify

Conflicts:

	src/community/importer/rest/src/test/java/org/geoserver/importer/rest/TaskResourceTest.java
allow serial binding to be used via system property
use ValidationException when reading transforms
add attributes to layer representation
cleanup, error handling, remove broken user tracking

extract running of import to method, handle validation exception
handle missing/disabled target store better

and remove unneeded try/catch block
fix broken test and behavior in LayerResource

testIndirectUpdateSRS was broken due to attribute encoding.
The problem was that TaskResource was using LayerResource to
copy the PUT'd layer/featuretype info resulting in an invalid
catalog state. Since the only supported change is SRS, remove
the call to CatalogBuilder that copies the ResourceInfo.

Also remove old, superfluous latLonBoundBox computation and
let this be handled elsewhere. Added assertion to the test to
verify this works.

Minor imports cleanup.

Conflicts:

	src/community/importer/rest/src/test/java/org/geoserver/importer/rest/RESTDataTest.java
move style computation ahead of other checks

when using a persistent store, it's possible that an upload
that is missing a SRS will not have the featuretype in it's metadata
map since that is marked transient to prevent serialization issues.

by computing the style first, we ensure that this is done while the
featuretype is still present

also add an exception if we cannot handle the resourceinfo class
check client provided workspace and store exist

it would be possible to create the importcontext with non-existing
workspace and target store otherwise causing failure later
write out json attribute binding correctly

and remove unsused imports
remove failing postgis tests, need to move

Conflicts:

	src/community/importer/rest/src/test/java/org/geoserver/importer/rest/TaskResourceTest.java
fix advanceId in memoryimportstore, test coverage
remove print stmt generating large xml output
copy resource properties specifically

fixes broken behavior after removing call to CatalogBuilder
update methods (that broke other behavior)
Mbtiles/geopkg: remove duplicated abstract class + fix various bugs
GEOS-6258 - Not considering http error codes < 400 as an error.

Patch provided by Rob Marianski.
GEOS-6261: promoting dxf community module to extension
Merge pull request #436 from NielsCharlier/mbtiles

Mbtiles/geopkg: remove duplicated abstract class + fix various bugs
Merge pull request #439 from mbarto/dxf_extension

GEOS-6261: promoting dxf community module to extension
Merge pull request #434 from ischneider/master-importer-from-2.3.x

Master importer from 2.3.x