improvement: add an indicator to show that the list of packages or nodes is empty

no indication always makes me question if the list is really empty or if there's something else going on. make it clear.

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: add a query indicator

the indicator is active as long as  query is running for an element. the indicator is on a per-field basis and not safe for multiple parallel queries. it indicates that a field is being fetched, either with or without pagination

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
add query indicator to frontend to be visible for nodes and packages

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
bugfix: fix loading indicator gif

include the loading indicator in the css since it didn't work correctly in webkit browsers. also show the loading indicator in the querying line for packages and nodes now.

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
fix loading indicator for packages

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
Merge pull request #42 from TelekomCloud/list-empty-indicator

List empty indicator