Provide operations to cancel retrieval of logs and to reload logs

Current Situation

• A number of optimizations have been added to improve the handling of logs.
• This includes the log view window to switch from log view to download of a log by hitting the "download" link in the log view window.

Desired Behavior

• Additional operations should be added next to the "download" link with the log view window:
  • Cancel: stop the current operation to retrieve a log (that might be too large for visualization with the log view window).
    • Clicking this link allows the user to subsequently use the "download" link without waiting for the log to be completely retrieved for display with the log view window.
    • Clicking the "download" link should include the same effect as hitting the "cancel" link: the current log retrieval is cancelled and download starts.
  • Reload: this operation is intended as a replacement for the "rolling log". We assume a log not to be completed as the task is still running. In this situation approx. every 5s a new log snapshot is created by the Master. Using the "reload" link allows to reload the log with the current log view window.
• The visible sequence of links with the log view window is: download reload cancel.