add support for general highlighting of concordance tokens based on a specified positional attribute value (or values)

[tomachalek]

1. in models/concordance/actions, define a new action HighlightTokensMatchingPosAttr where payload should contain at least a list of values (Array<string>) and positional attribute name (e.g. lemma).
2. add something like shadowLines:Array<Line> to the ConcordanceModelState
3. see the method changePage and use the initial part where const args is created and a respective ajax action is triggered and define a new method (e.g. loadShadowLines) which will replace all the args URL attributes (do not confuse with the constant args above) by the value of the positional attribute defined by the action from (1)
4. create a side-effect action HighlightTokensMatchingPosAttrDone which (once shadowLines are loaded) will go through all the "shadow" lines and compare respective values with the ones provided by action (1). In case of a match, go to the exact same position in lines and add some CSS class to highlight a matching token