Examples: Renamed applications to emphasis on use of GLFW as a platform framework + minor local tweaks

ImVector: Fixed insert() helper using the = operator (followup to be consistent with 4186c2c)

Fixed enum typo.

Examples: Vulkan: Fix missing subpass dependency ...

Without a dependency between pWaitDstStageMask (COLOR_ATTACHMENT_OUTPUT)
and the render-pass, the UNDEFINED -> COLOR_ATTACHMENT_OPTIMAL transition
might happen before the image is ready to be used.

Examples: Vulkan: Using VK_PRESENT_MODE_MAILBOX_KHR. Disable IMGUI_UNLIMITED_FRAME_RATE by default. Fixed warnings. (#1042)

Demo: Added more complete Combo demo. (#1658)

Nav: InputText: Allow editing text input fields with NavActivate (space). Not sure about that, on one hand it feels more consistent but you can't finish the editing with space to double space (activate + input space) could feel inconsistent. (#787)

Nav: Track nav input source more generally (gamepad vs keyboard) (#787) + update todos and demo tweaks

imgui.h: Various comments and tweaks.

imgui.h: Moved columns lower in the file. Various spacing changes and minor comments.

ImVector: Added copy/assign operators as helpers to ease cloning of data.

ImDrawList: Added Clone() helper function.

ImVector: resize() / push_back() use memcpy() as we are not supposed to be constructor/destructor/operator aware at all. (If we do need to rework ImVector). In turn this will allow us to define assign/copy operators.

ImVector: Using value_type consistently. Spacing.

Update TODO list, minor fix in Readme, comments, Clang -Weverything warning fix in imgui_draw.cpp under Windows.

Moved IM_NEW, IM_DELETE helpers to imgui.h for convenient use by back-ends and user code.

ImVector: Spacing, assert tweaks

Misc: Fix 111ea7a, GetStyleColorName() would assert, removed removed ImGuiCol defines (too much risk/complexity trying to silently ignore it).

Contributing: tweaks, mention screenshots more prominently.

Misc comments, todos + reintroduced removed ImGuiCol defines under !IMGUI_DISABLE_OBSOLETE_FUNCTIONS wrap.

Examples: Vulkan: Only resize swap chain and framebuffer once. (#1042)

Examples: Renamed glfw error callback for clarity.

Fixed resize window validation errors with removing frame prerender once and present last but one frame functionality. Frame rate is still similar.

Updated templates, added pull request template.

Style: CloseButton() now display a proper cross. Using Button colors for background. Removed ImGuiCol_CloseButton, ImGuiCol_CloseButtonActive, ImGuiCol_CloseButtonHovered as the closing cross uses regular button colors now. (#707)

Internals: Columns renaming fields

ImFont: Added FindGlyphNoFallback. Fixed MergeMode broken by 1ef1acb

Updated Changelog following merge of #1619 + fixed entry added to wrong version Changelog in 1ef1acb

Merge branch '2018-03-font_offset' into master2

Merge branch 'master' into font_offset