Ignore concerns in app/models/concerns

Fixes #1636
Use find_in_batches ActiveRecord feature to deal with large record sets in export.
Fix pledgie badge in readme.
Add support for fingerprint column
indicate that the mailing list is where to get support
pin mongoid to a specific version

https://github.com/ahoward/mongoid-grid_fs/pull/31 mongoid commit
cc7a0e709066aff444bc21cd9826e1568603934d broke mongoid-grid_fs so
we're pinning it to the commit before that.  we can un-pin mongoid
when mongoid-grid_fs becomes compatible with mongoid master.
remove ruby 1.9.2 from list of supported rubies

We evidently removed 1.9.2 from the set of rubies that we run in
Travis, so we shouldn't claim that we test with it.
pin rspec-core to a specific version

we were getting strange behavior only in jruby with rspec-core 2.14.6.
All of the tests would pass but the rake task would return 1 and cause
the Travis build to fail, for example
https://travis-ci.org/sferik/rails_admin/jobs/12765829.  On my machine
it failed intermittently but on Travis it was consistent.  2.14.5
works consistently so for now we'll pin it to that version.
Workaround for jruby rake issue. Refs #1804
Merge pull request #1803 from glebtv/patch-3

Add support for Paperclip's fingerprint column
Un-pin mongoid

Fixed by https://github.com/ahoward/mongoid-grid_fs/pull/32
Remove js link to ra.i18n.js. Closes #1798
Merge pull request #1783 from oruen/optimize-csv-converter

ActiveRecord csv export optimization.
support override of field help text via i18n.
provide default rails_admin help message so that it can be integrated in the overridden help text if desired. using e.g. "Team Name Help Text. %{help}"
Failing spec for #1714
Merge remote-tracking branch 'stympy/patch-1'
Point poltergeist to master. Refs #1804
use locale file from test project.
Merge pull request #1809 from ideadapt/field-help-i18n

Support override of field help text via i18n.