Upon arm, Mission Planner window resizes and fonts become unreadably small

#### Issue details
When reviewing a tlog history or when connect to a vehicle, upon arming, the Mission Planner window resizes itself to become smaller, and the fonts become unreadably small.

Manually making the window bigger again does not improve font size; font is still unreadable and small.

Screen capture video here:
https://youtu.be/7P9oNnTqcI0

System details:
I have reproduced this on 2 machines:
Mission Planner 1.3.59 on Win10 Surface Pro (screen resolution 2160x1440, Win10 “scale and layout” at 150% in display preferences
Mission Planner on Win8.1 Pro desktop (Screen resolution 3840x2160, Dell P2715Q monitor w/HDMI cable , Nvidia GeForce GTX 960 video card) Win 8 display “make text and other items smaller and larger” set at one click below largest

#### Version
Mission Planner 1.3.59

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

#### Airframe type
Fixed wing

#### Hardware type
Omnibus F4 Pro V2 Chibios

#### Logs
https://drive.google.com/open?id=1YisuWRScVH0eryLJrlezbH4t272j3ejX

Start by reproducing the issue in Mission Planner 1.3.59 on Windows with the reported high-DPI display scaling, then trace what changes when the vehicle is armed. Compare the window size and font rendering before and after arming; done means arming no longer shrinks the window or makes the fonts unreadably small.

Written by the indexing model from the issue text.