Fix katspaugh#1226 katspaugh#967: Refactoring of timeline plugin (kat…

…spaugh#1238)

* fixed linting issue in timeline plugin

* clean timeline container, so consecutive file loading does not produce empty canvases

* debounced the zoom event handler of the timeline plugin for improved perf

* added jsdoc comments to timeline plugin

* refactored timeline plugin for better performance and more consistency, added labelPadding and zoomDebounce params

* fixed wrong reference to event handler in destroy method