Develop v2.6 - Dynamic Initialization and Async Publishing

[goldbattle]

Key Changes

• Dynamic initialization has been added alongside the current static one.
  • New dependency requirement of ceres-solver to support the MLE refinement
  • Recovered covariance still requires some inflation (likely due to being close to identity)
  • Tested on existing datasets, seems to work reasonable well, but please let us know
  • Closes Dynamic Initialization Problem #204 and Running ETH3D Dataset #222
• The frontend now has two threads. The IMU will always publish the state odometry at its rate, along with recording the IMU readings. This should help deployment on real robots were the latency if key.
• Odometry publish is now in the local frame to match the ROS spec (fixes Odometry velocity in wrong frame #224)

Dynamic initialization is an implementation based on:

Dong-Si, Tue-Cuong, and Anastasios I. Mourikis. "Estimator initialization in vision-aided inertial navigation with unknown camera-IMU calibration." 2012 IEEE/RSJ International Conference on Intelligent Robots and Systems. IEEE, 2012.

• https://ieeexplore.ieee.org/abstract/document/6386235
• https://tdongsi.github.io/download/pubs/2011_VIO_Init_TR.pdf

Demo Youtube Video:
https://www.youtube.com/watch?v=eSQLWcNrx_I

demo.mp4