fix(olHelpers): text styles might contain text strings
fix(olHelpers): text styles might contain text strings

Text styles might contain a property 'text' which should be displayed directly.

```
{
   "text":{
      "text":"text text",
      "offsetX":0,
      "offsetY":0,
      "scale":3,
      "rotation":0,
      "fill":{
         "color":"rgba(255,128,0,1)"
      },
      "stroke":{
         "color":"rgba(128,128,128,1)",
         "width":1
      }
   }
}
```

Problem was that since 'text' is a style keyword, the previous implementation
looped into it, trying to convert the 'text text' string into an ol3 style
object.

chambleton/angular-openlayers-directive,mikostn/angular-openlayers-directive,yellingatcode/angular-openlayers-directive,kenkaohy/angular-openlayers-directive,milafrerichs/angular-openlayers-directive,ageblade/angular-openlayers-directive,StevenHeinrich/angular-openlayers-directive,sluyckx/angular-openlayers-directive,lewisjared/angular-openlayers-directive,TeChn4K/angular-openlayers-directive,juristr/angular-openlayers-directive,swfideas/angular-openlayers-directive,mikostn/angular-openlayers-directive,tormi/angular-openlayers-directive,tombatossals/angular-openlayers-directive,compso/angular-openlayers-directive,beyondlh/angular-openlayers-directive,lengpiseth/angular-openlayers-directive,juristr/angular-openlayers-directive,claycephas/angular-openlayers-directive,gaf-ag/angular-openlayers-directive,polesapart/angular-openlayers-directive,birdlifedk/angular-openlayers-directive