2.0.0-beta.9 round of fixing and small features

[a419d31] Reset to base configuration as fallback in invalid configurations
[c57d970] Move the catching in processConfiguration. Issue #182
[20b0e57] Use same warning message in invalid config. Issue #180
[a64d064] Fix typo in refactoring variables
[7b3801b] Treat prepend and load with different logic. Apply config array only if present. Issue #180
[4f20fb3] Improve warning messages in several lines and error with options parameter
[89d74ae] Improve documentation of ContextHelper, fix issue with config empty storage. Issue #182
[35c92b4] Refactor configuration tree options and enable read options from avanzu_admin_context. Issue #182
[d952d76] Add missing options breadcrumb_menu and main_menu. Issue #182
[aa58a10] Add font assets for admin lte
[6d8ade8] Fix issue with missing fonts copied. Issue #25
[201d899] Implement avanzu_html_start & avanzu_body_start blocks. Update doc
[8081f14] Update doc for kpn menu context for issue #184. Use default alias in conf
[a9dd301] Update links in knp menu doc
[563286a] Add PR welcome badge to Readme
[a7bd8f6] Add throughput graph in Readme
[236eed3] Add new bagde for symfony versions
[6a751fa] Create initial issue template
[58bc3a9] Fixed macros.html.twig
[75a7b44] Merge pull request #189 from SalvoS81/SalvoS81-minor-fix-1
[68752fa] Use alias for main menu
[e4eae91] Enable only the options if value is created not only set
[9fc2708] Update jquery version dependant of upstream AdminLTE. Issue #190
[938bb23] Enable datepicker in new bootstrap version. Issue #188
[bc5e392] Improve issue template
[fa3b3cd] Add small comment in code
[b956b72] Apply php-cs-fixer to new code
[fd88819] Fix wrong name for jquery
[91bd24c] Implement avanzu login box
[cbab11c] Implement login layout for use in fosuserbundle integration
[45b7197] Add docs to explain how to customize form_theme layout. Issue #39
[7fb8c8b] Improve docs about theme events and remove events not used
[039a2f1] Remove useless FormHelpExtension. Issue #165
[e9cd7f0] Detect OS version for uglify binaries. Issue #192
[4e27bfe] Remove space for datepicker class. Issue #188
[4421a4a] Start the messages translations feature
[5aaf768] Add translations keys to breadcrumb
[9501742] Add translations keys to default form
[578491b] Add spanish translation
[454b07c] Add build icon for travis
[c1d4737] Add PULL_REQUEST_TEMPLATE.md template file
[d6efea0] Move Issue template
[3efb490] Improve issue template
[9cbd5bd] Add RELEASE_CHECKLIST.md template