Mission/Survey related fixes

* If new Survey is set to altitude fixed value then use mission default
altitude
* If the user applies a new altitude to the entire mission change
surveys to fixed altitude and apply altitude

This way if the user switches away from manual the altitude is preserved

Correct hiding of heading on TAKEOFF command

Plan: Update home position when loading plan after vehicle already connected

GeoFenceManager: Add missing signals

Update for ArduCopter 3.5 release

Allow custom overrides of windows installer icons

Resume mission shows up at wrong times

Handle bogus lat/lon from ArduPilot

Stable fixes

iOS fixes

Hide "Save Path" as it breaks the UI in General Settings.

New polygon center calc

Hide wind rose until bugs are fixed

Delay creation of MAVLinkDecoder until it is needed

Helps battery life

Fix mode switching

PX4 Firmware plugin: First try to switch flight mode, then arm if successful - which is a lot safer than arming and then seeing if we can switch modes.

Firmwareplugin: Trim retry period to something that matches closer the users attention and is still long enough to allow for multiple heartbeats to pass through

Survey fixes