Pull class MimeInfoUpdater out of UpdateMimeInfoThread

* Pull out base class MimeEntryProcessor out of AppMetaMimeCreator.
* Pull class MimeInfoUpdater out of UpdateMimeInfoThread and derive it
  from MimeEntryProcessor.
* MimeInfoUpdater: Instead of BMimeType::GuessMimeType(), use
  Database::GuessMimeType() directly.
libroot_build: Fix incorrect skipDot check in find_dir_entry()

Would result in the _kern_open_parent_dir() failing for "/" and maybe in
other cases as well.
boot loader: print max heap usage info before entering kernel
boot loader: Add 256 KB additional heap

packagefs is using quite a bit additional memory for the MIME DB
entries and with all files identified.
MimeEntryProcessor: Add DoRecursively()

While Do() only process the specified entry, DoRecursively() also
recurses into directories.
Add te MimeInfoUpdater to libbe_build
mimeset: Complete custom mime DB support

* Don't require the first MIME DB directory to exist anymore. Database
  creates it anyway.
* Make use of MimeInfoUpdater to support updating MIME info with a
  custom MIME DB.
* Make use of MimeEntryProcessor::DoRecursively() to support recursive
  operation with a custom MIME DB.
AddDriversToContainer: Handle duplicate invocations

Since the same driver can be added in more than one category, in a few
cases AddDriversToContainer was invoked twice for the same target. Avoid
adding the driver twice to add-ons/kernel/drivers/bin in such a case.
Didn't really cause any problem, but no need to copy the file twice.
CopyDirectoryToContainer: fix typo in comment
Complete MIME related support for image/package creation

* Update MimeSet rule to use the MIME DB the build system creates.
* Add CreateAppMimeDBEntries rule and call it from Link for targets that
  might be applications that need to be registered with the MIME DB. For
  the target the rule is invoked with it creates a directory into which
  the entries for the types to be registered are written. The directory
  is associated with the target via the HAIKU_MIME_DB_ENTRIES variable.
* AddFilesToContainer: If a target is added that has MIME DB entries,
  also add those to the container.
* build_haiku_package: Call mimeset for the package contents.
Remove update_mime_info() support from libbe_build

It was there only for <build>mimeset, which is now always invoked with a
custom MIME DB and thus won't use the function anymore. We could
actually easily implement it using MimeInfoUpdater, if the MIME DB
directory the build system generates was compiled in.
Remove the no longer needed mime_update.sh post install script