Various fixes to plugin

Currently pinged line is now highlighted
Clear button to reset all information
Detailed information showing min/max and server url
NaN and -0 float values are now handled better
The initial values are now blank in the list view
Ping values are now persisted until closing unless cleared
Added a command-line build for releases
Added version/build number to plugin
Merge branch 'master' of https://github.com/kc5nra/ServerPingPlugin