Bug fix: suppression de isAbsurd et meilleure gestion des stylets (import des PR github #337 et #342)

Due to perfomance issues at openboard start, in a network-attached storage context, I had to find some (dirty) optimizations in order to counter-balance the huge response time of the directory scans performed when creating the documents tree (very huge in slowest machines (HDD, low CPU, with a thousand documents)). The simplest solution (I found) was to let the opening of metadatas fail, and to prevent any scanning. This implied to introduce the page-count as a metadata. As this issue is not encountered with a standard use of OpenBoard (with local documents), no update operation (of every document) should be necessary out of the described context

update 'updated-at' metadata when moving a document to trash (as it is done on the metadata.rdf file)

just need to delete documents, as these methods are only used when closing OpenBoard. Fix bad indexes issues

Update OpenBoard_it.ts

Create Messages_sk.properties

update proposal to lang DE

Update OpenBoard_sk.ts

fixed my own typo

This reverts commit 7dc58b7e.

This reverts commit adb884c8.

This reverts commit 410d0ff1.

added some relinks in Homebrew libs (absolute paths refering to other libs ... homebrew 2.0 issue ? osx upgrade issue ? xcode linker issue ?