Decide if we use another form tool instead of pyramid_simpleform

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We are actuality using pyramid_simpleform for form management. We need to give a try to alternatives likes Deform, WTForms, etc.. and decide if we keep simpleform or use something else.

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We will not try Deform as i do not see advantages compared to pyramid_simpleform.
WTForms seems to be a good alternative because is more understandable to Django users
and because it may have a better i18n support than pyramid_simpleform.

Actualy the only big problem with pyramid_simpleform is the i18n support (see #24)

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The i18n support of pyramid_simpleform is now working.
But, we may give a try to WTForms in a branch to see if it's better than pyramid_simpleform.

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Working on a WTForms branch.