The changelog is added as a model. Although it is meant to be displayed
with the licenses for Meshroom and AliceVision, the changelog model is
provided apart from the licenses' and then concatenated with it so they
are displayed together.
Accessible from main menu Help > About Meshroom, or by pressing "F1". Provides info about Meshroom version + useful links and related Open Source Licenses.
* load COPYING.md from Meshroom/AliceVision files (either provided with the standalone package or online) + translate them to HTML for display (added `markdown` package in requirements)
* request.js: centralize function to open file urls
* provide system info from MeshroomApp (exposed as contextProperty)