Log Analyses Graph breaks when adding too many CurveItems to be shown

#### Issue details
Steps to reproduce:
1. Run the application
2. Select "Telemetry Logs" CTA when the MissionPlanner GUI loads
3. Select the "Tlog > Kml or Graph" CTA
4. Load in a tlog file by clicking on the "Graph Log" CTA and selecting the tlog file
5. Notice that when clicking a large amount of CurveItems to be displayed (by checkmarking the right hand elements), the graph gets quite smaller and eventually dissapears.

Expected results: There should be a nicer way to handle listing CurveItem elements and their information without making the graph unreadable. My team's idea is to only have the GUI show 4 or so elements (so that the graph is still nicely proportioned) and to add a scrolling feature to see which CurveItems are being displayed.

Actual results: Adding to many CurveItems to the Log Analyses graph makes the graph unpleasant to read and also eventually makes the graph dissappear if selecting enough elements

Processor: Intel Core i7-3630QM CPU @ 2.40 GHZ

RAM: 8 GB

System type: 64-bit Operating System

OS: Windows 10

Notes:

#### Version
1 parent 7d3286e commit 12f6beea15233afac13b7c48d14238d347ad6a3d

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ + ] Rover
[ ] Sub

#### Airframe type
NA, will update this section on Tuesday 12/4/2018 with the correct information.

#### Hardware type
NA, will update this section on Tuesday 12/4/2018 with the correct information.

#### Logs
.tlog file is not supported

Reproduce the problem through the MissionPlanner GUI's “Telemetry Logs” and “Tlog > Kml or Graph” CTAs, then load a tlog and select many CurveItems. Inspect the Log Analyses graph and its CurveItem list. Done means selecting many items no longer makes the graph unreadable or disappear, with a usable way to view the selected items.

Written by the indexing model from the issue text.