Fix 3 warnings reported by GCC 8.1 of the following type
```src/client/gameui.cpp:191:43: warning: « void* memset(void*, int, size_t) » effacement d'un objet du type non trivial « struct GameUI::Flags »; use assignment or value-initialization instead [-Wclass-memaccess]
memset(&m_flags, 0, sizeof(GameUI::Flags));
```
* Android: Add zoom, minimap, and toggle chat button
Zoom button is put above jump button.
Minimap and toggle chat button are put in settings bar.
* Jump button is rotated down button
* Move three buttons on the right screen higher
* Android: Replace movement buttons with joystick
Replace movement control buttons (arrows at bottom left screen) with virtual joystick.
Joystick has 8 directions (same as keyboard). Basically, just map it to keyboard input.
Joystick applies only on left 1/3 of screen.
Joystick's position can be fixed by enabling fixed_virtual_joystick setting.
Three new images:
(1) placeholder joystick,
(2) joystick container (background), and
(3) joystick cursor.
Remove unused images: movement control buttons (*_arrow.png).
New data type: touch_gui_joystick_move_id
Joystick's fixed position is spaced one button size from bottom and from left of screen.
Remove unused variable: m_joystick_downlocation
* Implement new travis clang-tidy build step
* This step enable some rules and enforce one rule as error
* This permits to have some C++ quality rules based on clang & clang contributor guidelines
* Fix clang-tidy reported problems on push_back -> emplace_back
* Cleanup sound manager client
* Use some const refs
* Use auto on iterators
* Drop unused parameters
* Move sound_openal.* to client folder
* Move sound.cpp + OnDemandSoundFetcher to client/ folder + reorganize includes properly
* Server: delegate mod management & config to ServerModConfiguration (rename it to ServerModManager)
* Use c++11 range based loops
* Add unittests + experimental/default mod as a test case to permit testing mod loading in future tests
* Make InputHandler own the key cache
* Add a helper function InputHandler::cancelPressed to avoid multiple similar calls in game.cpp
* Move RandomInputHandler::step definition into cpp file
* Attempt to add registration confirmation
Using SRP auth mechanism, if server sent AUTH_MECHANISM_FIRST_SRP that means the player isn't exist.
Also tell player about the server and chosen username.
Local game has localhost as IP address of the server.
Add RenderingEngine::draw_menu_scene() to draw GUI and clouds background.
aborted -> connection_aborted
* Rewrite information message text
Client::promptConfirmRegister() -> Client::promptConfirmRegistration()
Allowing scrolling with the mousewheel when the vertical scrollbar is
hidden, unnecessarily exposes oversized containers and newlines at the
end of the text. For example try scrolling over the textareas in the
pause menu. This PR addresses the issue by requiring the scrollbar to be
visible before allowing the scrolling with the mousewheel.
