Initial commit
Add initial package.xml
plugins: Initial import px4flow.

Import px4flow plugin written by M.H.Kabir.
node: Initial import gcs_image_bridge.

In addition to `gcs_bridge` functions it sends imeges to GCS.
QGC receive it, but it constantly log this error:

    src/uas/UAS.cc 2093 Loading data from image buffer failed!
plugin: Add image_pub plugin.

TODO: image decode and publish.
Find why mavconn hangs on high speed io.
plugins: Add ctor initialization.

Coverity recommends init all data members.
plugins: Init ctor
plugin: param: erase invalidates iterator.

Real error found by coverity :)
Add ci badges to readme
plugin: sys_status: Decode sensor health field.

Fix #75.
plugin: sys_status: Add SYSTEM_TIME sync send.

Fix #78.
plugin: vision_speed: Initial import.

Fix #67.
launch: Use connection URL
launch: PX4 default ids=1,50.

Also waypoint plugin works (with first_pos_control_flight-5273-gd3d5aa9).
Issue #68.
plugins: replace initial memset with c++ initializer list
node: Make project buildable by clang.

Clang produce more readable errors and provide
some static code analysis, so i want ability to build mavros
with that compilator.
travis: enable clang build.
travis clang to old, fails on boost signals2 library. disable.
plugins: Replace boost mutexes with C++11.

Issue #80.
plugins: Replace Boost condition variables with C++11

Issue #80.