Bug 948040 - Back out the download manager from 1.3

This revert has been done removing 23 commits from the Download Manager feature
in chronological order, here are the bugs involved:

Revert "Bug 940294 - [Download Manager] Implement the flow when the user opens a file and this action fails from notifications"
This reverts commit aabc4f988bf457950cdd77a71f011398cecf3ca2.

Revert "Bug 946660 - [Download Manager] Downloading notifications should not be displayed in the toaster"
This reverts commit 1ee01682bf07d74769d247758228254fbdd81298.

Revert "Bug 935088 - [Download Manager] Download list implementation r=kaze, arcturus, evelyn"
This reverts commit 75f8f645f1489bc708f3407b0db4464ef73b5884.

Revert "Bug 945678 - [Download Manager] Implement shared flow when the user opens a file and this action fails"
This reverts commit d133b1aa704d71333f4bafaf9daa0ff496a65583.

Revert "Bug 941717 - [Download Manager] Implement a way of removing downloads"
This reverts commit 3f4f563d9c2858a55ebacd5b1f499e363559deda.

Revert "Bug 944639 - [Download Manager] The complete downloads have to be stored to maintain the history in the download list"
This reverts commit 22a85c46883f9113f5439a9f7315a8d2f13d9c06.

Revert "Bug 940290 - [Download Manager] Implement timestamps for download notifications"
This reverts commit 3443208657ba43038f76f10a2cb9055d1dba88a0.

Revert "Bug 935094 - [Download Manager] Download notifications"
This reverts commit 6a59916c6de77fe94a67222f5a20bada6b99e3ac.

Revert "Bug 945628 - [Download Manager] Discover storage name and relative path from absolute paths"
This reverts commit 3b5963d6d3fdd1fb936b128950df0c7f77b52dd9.

Revert "Bug 945668 - [Download Manager] Adapt shared components to Download API"
This reverts commit 3d9a38aa9d7d56bd96db75162ead29c9d9e31acc.

Revert "Revert "Bug 935094 - [Download Manager] Download notifications" for breaking Gaia UI Tests"
This reverts commit 4ad01a3200951315fc8e62904b114e1ea17a86ea.

Revert "Bug 935094 - [Download Manager] Download notifications"
This reverts commit 55d5a661d0ffef0bd9db3405912ba0d5ce3ae339.

Revert "Bug 941694 - [Download Manager] New library to store the complete downloads"
This reverts commit 36c5a4ff4927b14138c7afb5d5f81ee46ed6ec15.

Revert "Bug 940432 - [Download Manager] [DownloadLauncher] Discover mime type from file extenstion"
This reverts commit 40ec4393e4f49328ad9c9c28085de0a72982c601.

Revert "Bug 940966 - [Download Manager] [DownloadFormatter] The field started is startTime in the API"
This reverts commit 4714c799127932864935b01f42e9ffd35d364c97.

Revert "Bug 942424 - Fix broken comment format, replace "ﬁle" with "file""
This reverts commit 4b132bb2724bdf5f7aa87017c48138b481bf4f8d.

Revert "Bug 940291 - [Download Manager] Implement UIs to support when the user opens a file and this action fails"
This reverts commit e30c56b61020c702d01981d45c48a4ee2f336e0e.

Revert "Bug 937116 - [Download Manager] Create a utility library for common DOM Download operations r=kaze,crdlc"
This reverts commit f9a10c84616cbab4a80e3850a405564db26baacd.

Revert "Bug 938043 - [Download Manager] Refine the shared component DownloadUI"
This reverts commit ac5c3c772304a23fb6370164b0bcae1154ff9429.

Revert "[Download Manager] New shared component DownloadLauncher"
This reverts commit 9178ab60dd379b7116e96306607bc68921542beb.

Revert "Bug 935070 - [Download Manager] New shared component DownloadUI"
This reverts commit c07ea0c8e4e225d818c503f1364692cebe7758ba.

Revert "Revert "Merge pull request #13401 from crdlc/bug-935087""
This reverts commit b824c4ca99bb3e6921dae627cd5ecd6f94cafedf.

Revert "[Download Manager] Download list view skeleton"
This reverts commit 1e1018ed027a60d6668a420d0c4272326a1e7315.
Merge pull request #14748 from arcturus/backout-dm

Bug 948040 - Back out the download manager from 1.3