rewrite channel compare to java: make channel_selector parameterizable
rewrite channel compare to java: use simple ternary operator instead of c:choose
rewrite channel compare to java: ChannelPackagesCompare.do

rewrite of /network/software/channels/manage/packages/compare/index.pxt
rewrite channel compare to java: replaced <c:if> with ternary operator
rewrite channel compare to java: removed duplicated code
rewrite channel compare to java: fixed empty line after base channel
rewrite channel compare to java: added no package option to channel selector
rewrite channel compare to java: moved methods to IdComboDto class

to be able reuse them in PackageMergeDto
rewrite channel compare to java: ChannelPackagesCompareMerge.do

rewrite of /network/software/channels/manage/packages/compare/sync_preview.pxt
rewrite channel compare to java: use constant for standard "confirm" forward
rewrite channel compare to java: ChannelPackagesCompareMergeConfirm.do

rewrite of /network/software/channels/manage/packages/compare/sync_confirm.pxt
rewrite channel compare to java: moved duplicated code to ChannelPackagesBaseAction class
rewrite channel compare to java: removed obsoleted perl pages
removed unused compare_managed_channel_packages_provider()

which is unused after /network/software/channels/manage/packages/compare/*.pxt removal
removed unused sync_confirm_packages_in_set_provider()

which is unused after /network/software/channels/manage/packages/compare/*.pxt removal
removed unused managed_channel_merge_preview_provider()

which is unused after /network/software/channels/manage/packages/compare/*.pxt removal
removed unused sync_packages_to_channel_cb()

which is unused after /network/software/channels/manage/packages/compare/*.pxt removal