Add config to ignore keys case in sorting

[diabolusss]

At the moment (RBE v1.0.6 ) when saving, the keys are saved in alphabetical order, but fixed to a camelCase sorting.
The problem arises when properties contain keys with mixed case.

authorizationlevel.action.new = Nov� �rove\u0148 autorizace
authorizationlevel.admingroups = Spr�vcovsk� skupiny
authorizationlevel.admingroups.none = \u017d�dn�
authorizationlevel.amount = Mno\u017estv�
authorizationLevel.previousPeriodPayments.DAY = Den(-y)
authorizationLevel.previousPeriodPayments.HOUR = Hodina(-y)
authorizationLevel.previousPeriodPayments.MONTH = M\u011bs�c(-y)
authorizationLevel.previousPeriodPayments.YEAR = Rok(-y)
authorizationLevel.samePreviousRecipient = Stejn� p\u0159�jemce (intern� u\u017eivatel) jako v p\u0159edchoz�ch platb�ch

After save, it becomes:

authorizationLevel.previousPeriodPayments.DAY = Den(-y)
authorizationLevel.previousPeriodPayments.HOUR = Hodina(-y)
authorizationLevel.previousPeriodPayments.MONTH = M\u011bs�c(-y)
authorizationLevel.previousPeriodPayments.YEAR = Rok(-y)
authorizationLevel.samePreviousRecipient = Stejn� p\u0159�jemce (intern� u\u017eivatel) jako v p\u0159edchoz�ch platb�ch
authorizationlevel.action.new = Nov� �rove\u0148 autorizace
authorizationlevel.admingroups = Spr�vcovsk� skupiny
authorizationlevel.admingroups.none = \u017d�dn�
authorizationlevel.amount = Mno\u017estv�

Of course, mixed case keys in a file is not a good thing (by the way, 'force keys to lowercase' setting can be useful, too), i think that same keys with different case should be treated the same.

p.s. who knows, please, point me to where the sorting happens in the RBE code.