feat(monitor,API): change wmtsStyle for Graph layer

[ftoromanoff]

En lien avec le ticket RedMine#2075

Correction du flux WMTS pour QGIS et de la gestion du STYLE dans itowns

Correction de la régression #329

[coveralls]

Pull Request Test Coverage Report for Build 2656769430

• 31 of 31 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.009%) to 95.07%

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Totals
Change from base Build 2595189438:	-0.009%
Covered Lines:	6010
Relevant Lines:	6295

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💛 - Coveralls

[ftoromanoff]

Quand on charge un cache IR seul, les couches OPI et ortho apparaissent correctement. Par contre, la couche contour n'est plus visible.

Corrigé