add a server method to retrieve the classification of services
based on EDAM topics.
added services classification visualisation on client-side
refactored services classification

services classification can now be queried by topic or by operation
add comments and first round of "tree pruning"
code cleanup (comments, formatting, etc.)
correct css for services classification treeview
tree template cleanup
additional classification tree pruning.
correct tree directive to use only one <ul> per tree level
add toggle capability to classification tree
do not display services classification "root node"
optimize classification tree creation

do not query services collection repeatedly, instead load all of them
in a single dict.
add specific style for service link in classification tree
simplified classification tree generation and added search string

for now search string is only on service name.
remove debug print
send back empty array as classification tree if no result
avoid concurrent classification search requests

disable search filter input to avoid concurrent search requests.
initialise toggle state for trees to open if a filter is given

when searching for a service, if a query string has been provided,
open the resulting tree.
avoid double display of classification tree after searches

when the query string entered does not return any result then the
resulting DOM (the ng-repeat in classification.html) is sometimes
not emptied, resulting in a double classification afterwards. The
only workaround I found is to add an ui-if condition to the display
of the list.