This PR splits the GUI source files from the core source files. The immediate goal is to allow the CLI to require only a minimum number of dynamic libraries. The long term goal is to create an architectural boundary around the core module, in preparation of libkdbx.
* Selecting one or more entries to download icons always forces the download (ie, if a new URL exists the new icon will be downloaded and set)
* Instead of downloading for each entry, the web url's are scraped from the provided entries and only those urls are downloaded. The icon is set for all entries that share a URL. This is useful if a group contains many entries that point to the same url, only 1 download call will occur.
* The icon download dialog displays whether you are doing one entry, many entries, or an entire group. It is also modal so you have to dismiss it to use KeePassXC again.
* Moved DuckDuckGo fallback notice into the download dialog.
