Rebased: Allows field labels to be set in config

[felix1m]

see #203
credits to @maebert

[coveralls]

Coverage decreased (-0.03%) to 94.57% when pulling da8c391 on felix1m:develop into 8a14aba on mattupstate:develop.

[jonafato]

This failed to build for a few reasons:

• There are a few PEP8 formatting errors. These should be easy fixes.
• On Python 3, unicode is removed. This can be solved by conditionally using unicode or str depending version (e.g. sys.version_info[0] > 3).

[mattupstate]

You can use flask_security.utils.string_types and flask_security.utils.text_type instead of rolling your own check.

[jonafato]

@mattupstate +1 I knew that had to exist somewhere in the project but overlooked utils for some reason.

[felix1m]

someone still interested in getting this merged? Did not find the time so far..

[felix1m]

okay, i found the time, took only a second :)

[CatarinaPBressan]

Hello, is there any plans to merge this PR? I could really use this.

[jirikuncar]

It would be nice to mark the values with _(...) for better i18n support.