Remove skill strings from constants

[dylano]

There were duplicate declarations for the Scout branding strings (scout_strings.js and constants.js). This change removes them from the constants class since they are now passed in to the skill directly via the brand file.

Updated the integration tests to also read strings from the brand file (as specified in the STRING_BRAND env variable) so now tests will pass with both the Scout and Pocket brand files.

[coveralls]

Pull Request Test Coverage Report for Build 55

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 79.266%

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Totals
Change from base Build 50:	0.0%
Covered Lines:	379
Relevant Lines:	465

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💛 - Coveralls