Support for str_to_bool and parse_relative_time_string

[netsettler]

• New function misc_utils.str_to_bool
• New function lang_utils.parse_relative_time_string

[coveralls]

Pull Request Test Coverage Report for Build 3529977107

• 23 of 23 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 73.549%

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Totals
Change from base Build 3495907130:	0.07%
Covered Lines:	5803
Relevant Lines:	7890

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💛 - Coveralls